Hydrido iridium(III) complexes of azoaromatic ligands. Isolation, structure and studies of their physicochemical properties

Article abstract of DOI:10.1016/j.ica.2011.02.029

Reactions of 2-(arylazo)pyridine (L^a-c) with [IrCl ₃(PPh₃)₂] in two different solvents, viz. ethanol and toluene are reported. In refluxing toluene two new isomeric (mer and fac geometries) iridium complexes, ha

Full text of DOI:10.1016/j.ica.2011.02.029

Inorganica Chimica Acta 372 (2011) 168–174
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Inorganica Chimica Acta
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Hydrido iridium(III) complexes of azoaromatic ligands. Isolation, structure and
studies of their physicochemical properties
Manashi Panda a, Nanda D. Paul a, Sucheta Joy a, Chen-Hsiung Hung b, Sreebrata Goswami a,
⇑
a Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700 032, India
b Department of Chemistry, National Changhua, University of Education, Changhua, Taiwan 500, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Reactions of 2-(arylazo)pyridine (La–c) with [IrCl3(PPh3)2] in two different solvents, viz. ethanol and tol-
uene are reported. In refluxing toluene two new isomeric (mer and fac geometries) iridium complexes,
having molecular formula [IrCl3(PPh3)(L)] (1 and 2) have been isolated. The reaction in refluxing ethanol
yielded two new hydrido complexes of molecular formula [IrHCl2(PPh3)(L)] (3) and [IrHCl(PPh3)2(L)]Cl (4)
along with the compound 2. All the complexes have been thoroughly characterized by NMR, UV–Vis
spectroscopy, cyclic voltammetry and X-ray crystallographic analysis. The 1H NMR spectra of the hydrido
complexes 3 and 4 showed a doublet and a triplet signals at d À20.43 and À14.82 respectively due to cou-
Article history:
Available online 16 February 2011
Dedicated to Professor S.S. Krishnamurthy.
Keywords:
Azo-aromatics
Hydrido Ir(III) complexes
X-ray crystal structures
Physicochemical properties
pling with magnetically equivalent phosphorous nuclei. Strong trans influence of the p-acceptor ligands
guided the X-ray structural parameters; bonds trans to the these ligands are unusually long. Similar elon-
gation effect was also noted for the bonds trans to the coordinated hydrido ligand. UV–Vis–NIR spectrum
consisted of multiple transitions in the UV and visible regions. Cyclic voltammetry of each of these com-
plexes has exhibited a reductive response between À0.25 and À0.55 V, which has been assigned to azo-
ligand reduction. The compound 3, however, showed a quasireversible oxidative wave near 1.45 V, due to
IrIII/IrIV couple.
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
context of their activities as homogeneous catalysts [1–10] and
biological activities [41–44]. It may be worth noting here that we
The chemistry of transition metal hydrido complexes has re-
ceived increasing attention over the years as the possibilities of-
fered by these compounds for design of homogeneous catalyst as
recently have reported two novel mixed ligand chloro complexes
of L [32]. The first one is a chloro bischelated complex of iridium
where one of the two coordinated ligands (L) binds as an anionic
C, N-donor revealing a new coordination mode of L, while the other
one is a rare mixed ligand iridium(V) complex. In this work two
well as preparation of novel complexes [1–10]. The p-acceptor li-
gands such as carbonyl, mono and polydentate phosphines and
cyclopentadienyl groups play significant roles [10–14] in stabiliza-
tion of such complexes. Literature survey has however revealed
that the corresponding complexes containing N-donor ligands
[15–25] have been less attended. The influence of the ancillary li-
gand on the reactivity of M–H bond is of interest and the role of
N-donor ligands in this context is now emerging [25–28].
strong
p accepting ligands viz. L and triphenyl phosphine are used
to stabilize Ir–H complexes. This report discloses the results of the
reaction between [IrCl3(PPh3)2] [45] and the ligand L. The hydrido
complexes were successfully isolated from alcoholic reaction med-
ium (Scheme 1).
We have a long standing interest in the coordination chemistry
2. Results and discussion
of transition metal complexes of the
p-acceptor azoaromatic li-
gands [29–36]. The platinum group metal complexes of 2-(ary-
lazo)pyridine (abbreviated as L, Chart 1) ligand system have been
the subject of considerable interest because of their rich redox,
spectroscopic behavior, catalytic activities and isomerization reac-
tions [37–40,4–8,10]. Iridium complexes in general and the corre-
sponding hydrido complexes, in particular, are effective in the
2.1. Synthesis and characterization
The three ligands, viz. La, Lb and Lc differing with respect to sub-
stitution on the phenyl ring are used in this work. The ligands and
the isolated compounds are collected in Chart 1.
Reaction of [IrCl3(PPh3)2] and the ligand L in equimolar propor-
tion in toluene produced a brown solution which on chromato-
graphic purification and subsequent crystallization yielded two
⇑
Corresponding author. Tel.: +91 3324734971; fax: +91 3324732805.
E-mail address: icsg@iacs.res.in (S. Goswami).
pure compounds 1 and 2 of identical molecular formulae
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.02.029

M. Panda et al. / Inorganica Chimica Acta 372 (2011) 168–174
169
hydride. The coupling between hydrogen and phosphorous nucleus
generates this doublet pattern. In the complex 4 hydride resonance
appeared at d À14.82 as a triplet due to coupling with two magnet-
ically equivalent phosphorous nuclei [50,51]. The 1H NMR spectra
of all the complexes are submitted as the Supporting Information
(Figs. S5-8).
2.2. Crystal structure
Suitable crystals for X-ray structure determination of 1c, 2c, 3a
and 4c were obtained by slow diffusion of dichloromethane solu-
tions of the compounds into hexane. Oak Ridge thermal-ellipsoid
plot (ORTEP) and atom numbering schemes of the above com-
plexes are shown in Figs. 1–4, crystallographic parameters and se-
lected bond lengths are collected in Tables 1 and 2 respectively.
Structural analysis of 1c and 2c indeed confirmed their isomeric
nature. In both these complexes the central Ir- center is hexa-coor-
dinated and surrounded by three chlorides, a triphenylphosphine
and a bidentated azoaromatic ligand, Lc producing a distorted octa-
hedral environment. The complex 1c is meridional (mer) with re-
spect to the three coordinated Cl atoms while 2c is facial (fac). In
1c two chlorides are disposed trans occupying two axial positions,
while the PPh3 is trans to azo-N and one of the chlorides is trans to
the pyridyl-N. Simplified drawings of coordinated atoms in the two
reference complexes are shown in Chart 2 for comparison. The
equatorial plane of 2c is formed by the two mutually cis disposed
chlorine atoms, Cl(1)–Ir(1)–Cl(3), 89.06(6)° and the two chelating
nitrogen atoms of the diazo ligand with the bite angle, N(3)–
Ir(1)–N(1), 77.4(2)°, which is considerably lower than the ideal va-
lue for an octahedral geometry. The Ir–Cl lengths are significantly
affected by different trans influences [52–54] of the pyridyl-N/
azo-N and PPh3 ligands. For example, the Ir(1)–Cl(2) bond length
in 2c is trans to PPh3 and is consequently unusually long. The azo
bonds are within the normal range of coordinated azo ligands
[29–35,55].
The X-ray structure of 3a is similar to that of the
[IrCl3(PPh3)(Lc)] (1c), except that a hydride is coordinated to irid-
ium trans to pyridyl-N instead of a chloride ligand. The ligand La
binds iridium using N(1) and N(3) atoms and the chelate bite angle
is N(1)–Ir(1)–N(3), 74.83(7)°. Two chloride ligands occupy the
trans axial positions (Cl(1)–Ir(1)–Cl(2), 173.046(18)°). In the equa-
torial plane, the PPh3 ligand and azo-N are nearly trans disposed
with the angle P(1)–Ir(1)–N(1), 177.43(4)° and the pyridyl-N is
trans to the hydride (H(102)–Ir(1)–N(3), 173.0(8)°). The bulky
PPh3 group displaced away from the La ligand towards the smaller
hydride ligand. Notably the Ir–N(pyridine) distance is longer than
that observed in 1c and 2c (av. 2.069 Å), but is similar to that
(av. 2.150(5) Å) in [IrH2(PPh3)2(bpy)]. The strong trans influence
[52–54] of hydride is expected to cause lengthening of the trans
Ir–N bonds.
Chart 1. Ligands and corresponding iridium complexes.
[IrCl3(PPh3)(L)] in 45% and 25% yield respectively (Scheme 1).
These compounds are geometrical isomers (vide infra). The color
of the compound 1 is brown while that of the compound 2 is
greenish yellow.
In an identical reaction of [IrCl3(PPh3)2] with L in 1:1 molar ratio
in boiling ethanol produced a greenish brown solution which on
subsequent purification produced two new hydrido complexes of
molecular formula [IrHCl2(PPh3)(L)] (3) and [IrHCl(PPh3)2(L)]Cl
(4) along with the compound 2 as a minor product (yield: 8–
10%) (Scheme 1). An identical set of products were also obtained
when the reactions were carried out in toluene containing only a
few drops of ethanol. It is not surprising since alcoholic solvents
have commonly been used for the synthesis of metal–hydrido
complexes [46,47].
These complexes, 1–4 gave satisfactory elemental analyses (cf.,
Experimental). Electrospray mass spectra of the complexes corrob-
orate with their formulations as described above. For example, the
complexes 1a, 2b, 3b and 4b showed intense peaks due to the
molecular ion [1a + Na]+, [2b + Na]+, [3b + Na]+ and [4b À Cl]+ at
m/z, 766, 780, 746 and 950 amu, respectively. Notably, the experi-
mental spectral features of the complexes correspond very well to
the simulated isotopic pattern for the given formulations. Repre-
sentative spectra of all the complexes along with the simulated
spectra are submitted as Supporting Information, Figs. S1-4.
The complexes posses S = 0 ground state, as determined by
magnetic susceptibility measurements at room temperature. These
showed resolved 1H NMR spectra in CDCl3: strong intensity peaks
were observed in the region d 7.99–7.90 and 7.44–7.32 due to the
presence of coordinated PPh3 ligand [48–49] Some resonances
originated from the coordinated L overlapped with that of PPh3.
The peaks in the range d 8.82–7.47 and 7.84–7.06 are assigned to
pyridyl and phenyl resonances, respectively. The most notable
observation in the spectrum of 3 is the appearance of a distinct
doublet at d À20.43, which confirms the presence of coordinated
Scheme 1. Syntheses of the complexes.

170
M. Panda et al. / Inorganica Chimica Acta 372 (2011) 168–174
Fig. 1. An ORTEP and atom numbering scheme for mer-[IrCl3(PPh3)(Lc)](1c).
Hydrogen atoms are not shown for clarity. Thermal ellipsoids are shown in 30%
probability.
Fig. 3. An ORTEP and atom numbering scheme for [IrHCl2(PPh3)(La)](3a). Hydrogen
atoms are not shown for clarity. Thermal ellipsoids are shown in 30% probability.
Fig. 2. An ORTEP and atom numbering scheme for fac-[IrCl3(PPh3)(Lc)](2c).
Hydrogen atoms are not shown for clarity. Thermal ellipsoids are shown in 30%
probability.
Fig. 4. An ORTEP and atom numbering scheme for the cationic part of
[IrHCl(PPh3)2(Lc)]Cl(4c). Hydrogen atoms are not shown for clarity. Thermal
ellipsoids are shown in 30% probability.
The structure of the cationic part of the compound 4c consists of
nearly planar IrN2HCl moiety with a bent P(1)–Ir(1)–P(2)
a
(166.10(6)°) grouping perpendicular to this plane. The bidentate li-
gand Lc chelates the iridium ion through N(1) and N(3) with a bite
angle N(1)–Ir(1)–N(3), 76.0(2)°. The octahedral coordination, typi-
cal of the Ir(III) complexes, is appreciably distorted because of che-
lation and very different bulkiness of the ligands. As a consequence
of smallest occupancy of the hydride ligand, the two trans PPh3
groups bent towards hydride to minimize the steric repulsion
resulting the P(1)–Ir(1)–P(2) angle much smaller than 180°. The
Ir(1)–N(pyridine) length (2.125(5) Å), which is trans to the hydride
ligand, is elongated considerably as expected [52–54]. Rest of the
structural parameters are in the normal range.
2.3. Electronic spectra
All the compounds 1–4 are freely soluble in non-polar solvents
like dichloromethane, chloroform and their electronic spectra

M. Panda et al. / Inorganica Chimica Acta 372 (2011) 168–174
171
Table 1
Crystallographic Data of 1c, 2c, 3a and 4c.
1c
2c
3a
4c
Empirical formula
Molecular mass
Temperature (K)
Crystal system
Space group
a (Å)
C
29H23Cl4IrN3P
C29H23Cl4IrN3P,O
794.49
173
Trigonal
P31
9.8210(1)
9.8210(1)
26.3302(7)
90
C29H25Cl2IrN3P
709.61
293
Monoclinic
P21/n
17.6463(10)
9.3033(5)
18.1635(10)
90
C47H39Cl2IrN3P2, 0.5(Cl), 0.5(Cl)
1006.32
150
Monoclinic
C2/c
32.9255(10)
15.0264(4)
23.4681(7)
90
778.49
150
Monoclinic
P21/c
11.4928(2)
15.1937(3)
16.7995(3)
90
b (Å)
c (Å)
a
(°)
b (°)
100.099(1)
90
2888.05(9)
4
90
120
2199.36(7)
3
1.800
114.221(1)
90
2719.4(3)
4
129.948(2)
90
8901.2(5)
8
c
(°)
V (Å3)
Z
Dcalc. (g/cm3)
1.791
1.733
1.502
Cryst. dimens. (mm)
h Range for data coll (°)
Goodness-of-fit (GOF)
Reflns. collected
Unique reflns.
0.18 Â 0.10 Â 0.08
1.8, 30.0
1.00
31292
8436
À0.83, 0.63
R1 = 0.0231
wR2 = 0.0490
0.20 Â 0.12 Â 0.08
2.3, 30.0
0.99
22989
8268
À2.38, 3.46
R1 = 0.0419
wR2 = 0.0879
0.22 Â 0.14 Â 0.08
2.1, 30.1
0.79
33928
7986
À1.15, 0.73
R1 = 0.0191
wR2 = 0.0521
0.10 Â 0.04 Â 0.03
1.6, 30.0
1.02
57261
12992
À2.34, 6.56
R1 = 0.0566
wR2 = 0.1739
Largest diff. between peak and hole (e ÅÀ3
)
Final R indices [I > 2r(I)]
Table 2
Selected Bond Lengths of 1c, 2c, 3a and 4c.
Bond
1c
2c
3a
4c
Ir1–N1
Ir1–N3
Ir1–P1
Ir1–Cl1
2.084(2)
2.051(18)
2.325(6)
2.360(6)
2.359(6)
2.357(6)
1.263(3)
2.011(5)
2.003(6)
2.316(16)
2.340(17)
2.403(15)
2.356(17)
1.305(7)
2.098(18)
2.160(19)
2.273(5)
2.362(6)
2.341(6)
1.490(2)
1.262(3)
2.003(5)
2.125(5)
2.365(16)
2.372(14)
2.338(17)
1.600(11)
1.281(7)
Ir1–Cl2/P2a
Ir1–Cl3/Hb
N2–N1
a
For 4C.
For 3a and 4c.
b
Fig. 5. Electronic spectra of 1a (black), 2a (green), 3a (brown) and 4a (violet). (For
interpretation of the references to color in this figure legend, the reader is referred
to the web version of this article.)
by two weak transitions at 485 nm (
560 nm
ca. 800 MÀ1 cmÀ1), the isomeric compounds
[IrCl3(PPh3)(L)], 2 on the other hand showed a broad transition at
around 400 nm (
, ca. 8500 MÀ1 cmÀ1) along with two weak tran-
sitions near 460 nm ( , ca.
, ca. 3570 MÀ1 cmÀ1) and 630 nm (
500 MÀ1 cmÀ1). The hydrido complexes [IrHCl2(PPh3)(L)], 3 exhib-
ited an intense and broad transition at 360 nm ca.
15975 MÀ1 cmÀ1), two shoulders at 400 and 336 nm along with a
weak transition at long wavelength region, 515 nm ca.
2190 MÀ1 cmÀ1). The compounds [IrHCl(PPh3)2(L)]Cl, 4 showed a
broad transition near 400 nm (
, ca. 13795 MÀ1 cmÀ1) along with
e
, ca. 1885 MÀ1 cmÀ1) and
(e,
e
e
e
(e,
(e,
e
two weak transitions at 460 nm (e, ca. 4985) and 565 nm (e, ca.
780 MÀ1 cmÀ1). Representative UV–Vis spectra are displayed in
Fig. 5 and spectral data are collected in Table 3.
Chart 2. Geometries of the complexes 1, 2, 3 and 4.
The transitions of high intensities at the lower energy part of
the spectra are presumably due to metal to ligand charge transfer
(MLCT) [48,49]. The weaker absorption tails exhibited by the irid-
ium complexes, 2 and 4, in the lower energy region may be as-
were recorded in dichloromethane solution. The compounds
[IrCl3(PPh3)(L)], 1 showed an intense absorption near 380 nm
(e
, ca.10775 MÀ1 cmÀ1) and two shoulders at 415 nm (
e
, ca.
6085 MÀ1 cmÀ1) and 363 nm (
e
, ca. 9610 MÀ1 cmÀ1) followed
cribed to forbidden 3MLCT (d (Ir)–p⁄(ligand)) transitions [56].
p

172
M. Panda et al. / Inorganica Chimica Acta 372 (2011) 168–174
Table 3
Electronic spectral data.
Compound
Electronic Spectraa [kmax/nm ( /MÀ1 cmÀ1)]
e
[IrCl3(PPh3)(L1a)](1a)
560(800), 485(1885), 413(6085)b, 380(10775),
363(9610)b, 297(6270), 228(32855)
558(825), 485(2045), 422(6830)b, 384(10060),
297(6280), 230(35210)
[IrCl3(PPh3)(L1b)](1b)
[IrCl3(PPh3)(L1c)](1c)
[IrCl3(PPh3)(L1a)](2a)
[IrCl3(PPh3)(L1b)](2b)
[IrCl3(PPh3)(L1c)](2c)
[IrHCl2(PPh3)(L1a)](3a)
[IrHCl2(PPh3)(L1b)](3b)
[IrHCl2(PPh3)(L1c)](3c)
564(785), 485(2010), 425(6575)b, 383(10585),
365(6945)b, 298(7080), 230(33970)
632(470), 462(3570)b, 417(8540)b, 393(9530),
312(5925), 230(30740)
630(495), 465(3700)b, 405(9350), 310(5235),
228(31690)
633(466), 460(3305)b, 370(7515), 310(5840),
228(29460)
515(2190), 400(7800)b, 362(15975), 336(14715)b,
228(39070)
511(2065), 406(8120)b, 367(14210), 334(12135)b,
230(35250)
503(1905), 329(10355), 228(38510)
[IrHCl(PPh3)2(L1a)]Cl(4a) 565(780), 456(4985)b, 408(13795)b, 391(14370),
Fig. 6. Segmented cyclic voltammograms of 1a (black), 2a (green), 3a (brown) and
4a (violet). (For interpretation of the references to color in this figure legend, the
reader is referred to the web version of this article.)
273(28555), 235(45260)
[IrHCl(PPh3)2(L1b)]Cl(4b) 565(875), 457(5775)b, 403(13285), 273(26305),
236(42230)
[IrHCl(PPh3)2(L1c)]Cl(4c) 564(890), 460(4080)b, 395(10695), 273(24690),
235(41485)
fac-isomer is more accessible to reduction than the corresponding
mer-isomer. On the other hand, voltammograms of the hydrido
complexes, [IrHCl2(PPh3)(L)], 3 and [IrHCl(PPh3)2(L)]Cl, 4 also con-
sisted of a reversible cathodic response but have a significant dif-
ference in E0 values. While the compound 4 exhibited a reductive
wave at À0.27 V, the response in the compound 3 moved cathodic
to À0.55 V indicating that the cationic compound 4 is more easily
reduced than the neutral compound 3. The one-electron redox re-
sponse has been confirmed by constant-potential electrolysis for
all the reversible waves. The redox potentials are found to be sen-
sitive to the nature of substitution on the phenyl ring. Thus, a sys-
tematic anodic shift of the redox potentials was observed upon
moving from electron donating –Me substituted ligand (Lb) com-
plex to the electron withdrawing Cl ligand (Lb) complex (Table
3). It may be noted here that the free ligand L is known to undergo
two-step reductions at À1.31 and À1.57 V [29–35]. The response in
the cathodic potentials for the above complexes are ascribed to the
reduction of L ligand. In all the complexes, reported herein, the po-
tential of the reduction process is shifted toward at more positive
value because of the strong electronic pull of the metal ion (IrIII).
After coordination the azo ligand becomes electron deficient and
hence is more easily reduced than the free (uncoordinated) ligand.
Similar trend has been noted before in the several reported com-
pounds of L. However, we failed to observe the second reduction
process of the coordinated azo-function which possibly falls out-
side the accessible voltage window. In addition, the compound 3
also showed an irreversible oxidative wave with no cathodic coun-
ter part at 1.45 V. Comparing with previously reported Ir–L com-
plexes [32] this is assigned to a IrIII/IrIV process.
a
In dichloromethane.
Shoulder
b
Table 4
Electrochemical dataa.
Compound
Oxidation E b/V
Reduction ÀE b/V
½
½
(D
Ep/mV)
(DEp/mV)
[IrCl3(PPh3)(L1a)](1a)
[IrCl3(PPh3)(L1b)](1b)
[IrCl3(PPh3)(L1c)](1c)
[IrCl3(PPh3)(L1a)](2a)
[IrCl3(PPh3)(L1b)](2b)
[IrCl3(PPh3)(L1c)](2c)
[IrHCl2(PPh3)(L1a)](3a)
[IrHCl2(PPh3)(L1b)](3b)
[IrHCl2(PPh3)(L1c)](3c)
[IrHCl(PPh3)2(L1a)]Cl(4a)
[IrHCl(PPh3)2(L1b)]Cl(4b)
[IrHCl(PPh3)2(L1c)]Cl(4c)
0.41(110)
0.42(90)
0.36(100)
0.32(90)
0.34(90)
0.30(110)
0.55(100)
0.58(120)
0.50(120)
0.27(90)
0.32(90)
0.24(100)
1.45c
1.48c
1.55c
a
Conditions: solvent, dichloromethane; supporting electrolyte, NBut4ClO4
(0.1 M); working electrode, platinum for oxidation and reduction processes; ref-
erence electrode, SCE; solute concentration, ca. 10À3(M); scan rate, 50 mV sÀ1
.
b
E
½
= ½(Epa + Epc),
D
Ep = Epa À Epc in mV (Epa = anodic peak potential, Epc
= cathodic peak potential).
c
Irreversible value corresponds to Epa
.
The strong transitions in the UV region (<350 nm) are attributable
to intra-ligand charge transfer transitions [29–35].
2.4. Redox properties
3. Conclusion
The redox behavior of all the reference complexes was studied
by cyclic voltammetry in dichloromethane (0.1 M TBAP), in the po-
tential range +1.5 to À1.5 V, using a platinum working electrode.
The potentials are referenced to the saturated calomel electrode
(SCE) and the data are collected in Table 4. Segmented voltammo-
grams (cathodic sweep) of the representative compounds are dis-
played in Fig. 6.
Two novel mixed ligand Ir(III) hydrido complexes have been
synthesized using two strong p-acidic ligands, viz. 2-(arylazo)pyr-
idine and PPh3 in EtOH. Non-alcoholic solvent, toluene failed to
produce the hydrido complexes and two new isomeric non-hydri-
do complexes were obtained. Alcoholic solvents play the pivotal
role in Ir–H bond formation. These complexes constitute new
Nature of the voltammograms of the compounds mer-
[IrCl3(PPh3)(L)], 1 and fac-[IrCl3(PPh3)(L)], 2 is similar. An electro-
chemically reversible cathodic response near À0.4 V was observed
for the compound 1 and that for 2 was observed near À0.3 V. This
shift of potential indicates that the acceptor level (LUMO) in the
examples of Iridium complexes with strong p accepting N-donor li-
gands where the ligand L stabilizes the iridium(III) state preferably.
All the complexes show rich physicochemical properties. Hydride
complexes with N-donor ligands are important in the field of reac-
tivity studies of Ir–H bonds. Our work in this area is ongoing.

M. Panda et al. / Inorganica Chimica Acta 372 (2011) 168–174
173
C29H23N3Cl4PIr: C, 44.74; H, 2.98; N, 5.40. Found: C, 44.77; H,
4. Experimental
3.03; N, 5.36.
[IrCl3(PPh3)(Lc)](2c). Yield: 25%, FT-IR (KBr, cmÀ1): 1595
4.1. Materials
[m(C@N)], 1380 [m [m(PPh3)], ESI-
(N@N)], 530, 595 and 750 cmÀ1
MS, m/z: 801 [M+Na]+. Anal Calc. for C29H23N3Cl4PIr: C, 44.74; H,
2.98; N, 5.40. Found: C, 44.76; H, 3.04; N, 5.42.
IrCl3ÁxH2O was obtained from Arora Matthey and was digested
twice with concentrated HCl before use. Solvents and chemicals
used for syntheses were of analytical grade and used as received.
Supporting electrolyte (TEAP) [57] and solvents for electrochemical
work were obtained as before. 2-(Arylazo)pyridines were prepared
following the reported procedure [58]. Caution! Perchlorate salts
have to be handled with care and with appropriate safety precautions.
4.3.2. Reaction of [IrCl3(PPh3)2] with 2-(Arylazo)pyridine (La–c) in
ethanol
4.3.2.1. Isolation of [IrCl3(PPh3)(La)] (2a), [IrHCl2(PPh3)(La)] (3a),
[IrHCl(PPh3)2(La)]Cl (4a). The reaction of [IrCl3(PPh3)2] with La in
1:1 molar ratio in boiling ethanol produced a greenish brown
solution in about 3 h. Three pure compounds of molecular formula
[IrCl3(PPh3)(La)] (2a), [IrHCl2(PPh3)(La)] (3a) and [IrHCl(PPh3)2
(La)]Cl (4a) were isolated from the crude mass.
4.2. Methods
UV–VIS–NIR absorption spectrum was recorded on a Perkin–
Elmer Lambda 950 UV/VIS spectrophotometer. NMR spectra were
taken on a Bruker Avance DPX 300 spectrometer. Infrared spectra
were obtained using a Perkin–Elmer 783 spectrophotometer. Cyc-
lic voltammetry was carried out in 0.1 M Bu4NClO4 solutions using
a three-electrode configuration and a PC-controlled PAR model
273A electrochemistry system. The E1/2 for the ferrocenium–ferro-
cene couple under our experimental condition was 0.39 V. A Per-
kin–Elmer 240C elemental analyzer was used to collect micro
analytical data (C, H, N).
The compounds were purified and isolated from the crude mass
on preparative silica-gel TLC plate. The brown compound 3 was
eluted first using toluene–chloroform (1:9) solvent mixtures. The
other two compounds 2 and 4 moved successively and were eluted
with chloroform–acetonitrile (4:1) solvent mixture. The com-
pounds were obtained in different yields depending on the ligands
used. Their yields and characterization data are as follows. Notably
the sample of 2 obtained from these reactions has exactly identical
analytical and spectral properties of the authentic sample of 2 ob-
tained from the reactions described above.[IrCl3(PPh3)(La)](2a).
Yield: 10%.
4.3. Syntheses
[IrHCl2(PPh3)(La)](3a). Yield: 25%, FT-IR (KBr, cmÀ1): 1600
[m(C@N)], 1390 [m(N@N)]. 535, 695 and 750 [m(PPh3)], ESI-MS, m/
4.3.1. Reaction of [IrCl3(PPh3)2] with 2-(arylazo)pyridine (La–c) in
toluene
z: 732 [M+Na]+. Anal Calc. for C29H25N3Cl2PIr: C, 49.08; H, 3.55;
N, 5.92. Found: C, 49.11; H, 3.51; N, 5.95.
4.3.1.1. Isolation of [IrCl3(PPh3)(La)](1a), [IrCl3(PPh3)(La)](2a). The
reaction mixture of [IrCl3(PPh3)2] and the ligand La in equimolar
proportion was heated at reflux in toluene for 3 h. During this per-
iod, initial orange color of the mixture became brown. Two pure
compounds 1 and 2 of identical molecular formulae [IrCl3(PPh3)(-
La)] were isolated from the crude mass.
[IrHCl(PPh3)2(La)]Cl(4a). Yield: 30%, FT-IR (KBr, cmÀ1): 2140–
2185 [m(Ir–H)], 1590 [m(C@N)], 1385 [m(N@N)]. 520, 695 and 750
[
m
(PPh3)], ESI-MS, m/z: 935 [MÀCl]+. Anal Calc. for C47H40N3Cl2P2Ir:
C, 58.08; H, 4.15;
N 4.32. Found: C, 58.12; H, 4.17; N,
4.35.[IrCl3(PPh3)(Lb)](2b). Yield: 8%.
[IrHCl2(PPh3)(Lb)](3b). Yield: 25%, FT-IR (KBr, cmÀ1): 1600
The pure compounds were isolated from the crude mixture on
preparative TLC (Thin Layer Chromatography) silica-gel plate. It
was first eluted with toluene–chloroform (1:9) solvent mixture.
The compound 1 moved first as the top brown band and was iso-
lated. Another band, greenish yellow in color, was then separated
out on elution with chloroform–acetonitrile (4:1) solvent mixture.
The compound 2 was obtained by the evaporation of the above elu-
ate. The yields and characterization data of 1a and 2a are as
follows.
[m(C@N)], 1390 [m(N@N)]. 535, 695 and 750 [m(PPh3)], ESI-MS, m/
z: 746 [M+Na]+. Anal Calc. for C30H27N3Cl2PIr: C, 49.79; H, 3.76;
N, 5.81. Found: C, 49.74; H, 3.80; N, 5.79.
[IrHCl(PPh3)2(Lb)]Cl(4b). Yield: 30%, FT-IR (KBr, cmÀ1): 2140–
2185 [m(Ir–H)], 1590 [m(C@N)], 1385 [m(N@N)]. 520, 695 and 750
[
m
PPh3)], ESI-MS, m/z: 949 [MÀCl]+. Anal Calc. for C48H42N3Cl2P2Ir:
C, 58.47; H, 4.29;
N 4.26. Found: C, 58.45; H, 4.32; N,
4.23.[IrCl3(PPh3)(Lc)](2c). Yield: 10%.
[IrHCl2(PPh3)(Lc)](3c). Yield: 25%, FT-IR (KBr, cmÀ1): 1600
[IrCl3(PPh3)(La)](1a). Yield: 45%, FT-IR (KBr, cmÀ1): 1615
[m(C@N)], 1390 [m(N@N)]. 535, 695 and 750 [mPPh3)], ESI-MS, m/
[
m
(C@N)], 1405 [
m
(N@N)]. 530, 695 and 745 [
m
(PPh3)], ESI-MS, m/
z: 708 [MÀCl]+. Anal Calc. for C29H24N3Cl3PIr: C, 46.81; H, 3.25;
N, 5.65. Found: C, 46.79; H, 3.28; N, 5.61.
z: 766 [M+Na]+, Anal Calc. for C29H24N3Cl3PIr: C, 46.82; H, 3.25;
N, 5.65. Found: C, 46.85; H, 3.22; N, 5.64.
[IrHCl(PPh3)2(Lc)]Cl(4c). Yield: 30%, FT-IR (KBr, cmÀ1): 2140–
[IrCl3(PPh3)(La)](2a). Yield: 25%, FT-IR (KBr, cmÀ1): 1595
2185 [m(Ir–H)], 1590 [m(C@N)], 1385 [m(N@N)]. 520, 695 and 750
[
m(C@N)], 1380 [
m
(N@N)], 530, 595 and 750 cmÀ1
[m
(PPh3)], ESI-
[
m
(PPh3)], ESI-MS, m/z: 969 [MÀCl]+. Anal Calc. for C47H39N3Cl3P2Ir:
MS, m/z: 766 [M+Na]+. Anal Calc. for C29H24N3Cl3PIr: C, 46.82; H,
3.25; N, 5.65. Found: C, 46.79; H, 3.27; N, 5.62.
C, 56.09; H, 3.91; N 4.18. Found: C, 56.12; H, 3.96; N, 4.21.
Other substituted complexes (1b, 2b and 1c, 2c) were similarly
synthesized using the Lb and Lc ligands in place of La. Their yields
and characterization data are as follows.
4.4. Crystallographic measurements
Crystallographic data for the compounds 1c, 2c, 3a and 4c are
collected in Table 1. Suitable X-ray quality crystals of all these
are obtained by slow diffusion of a dichloromethane solution of
the compound into hexane.
All data were collected on a Bruker SMART APEX-II diffractometer,
equipped with graphite monochromated Mo Ka radiation
(k = 0.71073 Å), and were corrected for Lorentz-polarization effects
[59,60]. 1c: A total of 31292 reflections were collected, out of
which 8436 are unique (Rint = 0.0357) reflections satisfying the
[IrCl3(PPh3)(Lb)](1b). Yield: 45%, FT-IR (KBr, cmÀ1): 1615
[m(C@N)], 1405 [m(N@N)]. 530, 695 and 745 [m(PPh3)], ESI-MS, m/
z: 780 [M+Na]+. Anal Calc. for C30H26N3Cl3PIr: C, 47.53; H, 3.46;
N, 5.54. Found: C, 47.56; H, 3.50; N, 5.51.
[IrCl3(PPh3)(Lb)](2b). Yield: 25%, FT-IR (KBr, cmÀ1): 1595
[
m
(C@N)], 1380 [
m
(N@N)], 530, 595 and 750 cmÀ1
[
m
(PPh3)], ESI-
MS, m/z: 780 [M+Na]+. Anal Calc. for C30H26N3Cl3PIr: C, 47.53; H,
3.46; N, 5.54. Found: C, 47.57; H, 3.49; N, 5.50. [IrCl3(PPh3)(Lc)](1c).
Yield: 45%, FT-IR (KBr, cmÀ1): 1615 [
m
(C@N)], 1405 [
m
(N@N)]. 530,
I > 2r(I) criterion and were used in subsequent analysis. 2c: A total
695 and 745 [
m
(PPh3)], ESI-MS, m/z: 801 [M+Na]+. Anal Calc. for
of 22989 reflections were collected, out of which 8268 were unique

174
M. Panda et al. / Inorganica Chimica Acta 372 (2011) 168–174
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The research was supported by Council of Scientific and Indus-
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