Use of a Ru/Os-CO-diiodide precursor to synthesize heteroleptic 1-alkyl-2-(arylazo)imidazole complexes: The structural characterization, electrochemistry and catalytic activity

Article abstract of DOI:10.1016/j.poly.2012.11.013

Trans-(I,I)-[MI₂(CO)₂(RaaiR′)] (M = Ru, Os) (RaaiR′ = 1-alkyl-2-(arylazo)imidazoles) complexes have been synthesized by the reaction of RaaiR′ and [Ru(CO)₄I₂] or [Os(CO)₄I₂] in acetonitrile solution and the complexes have been characterized by elemental analysis and spectral (FT-IR, UV-Vis, ¹H NMR) data. The structural confirmation has been determined by single crystal X-ray diffraction of trans-(I,I)-[MI₂(CO) ₂(HaaiEt)] (M = Ru, 3b; Os, 5b) (HaaiEt = 1-ethyl-2-(phenylazo) imidazole) and has shown a distorted octahedral geometry with a trans-I,I and cis-CO, CO configuration. The complexes show a M(III)/M(II) couple and the reduction of the chelated azoimine ligand. These complexes act as catalysts in the oxidation of PhCH₂OH to PhCHO, 2-butanol (C₄H ₉OH) to 2-butanone, cyclopentanol (C₅H₉OH) to cyclopentanone and cyclohexanol to cyclohexanone by N-methylmorpholine-N-oxide (NMO). The molecular orbital diagram has been drawn by density functional theory (DFT) using the optimized geometry from the single crystal X-ray parameters. The assignments of electronic spectra have been carried out by TD-DFT calculations both in the gas and acetonitrile phases.

Full text of DOI:10.1016/j.poly.2012.11.013

Polyhedron 50 (2013) 246–254
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Polyhedron
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Use of a Ru/Os-CO-diiodide precursor to synthesize heteroleptic
1-alkyl-2-(arylazo)imidazole complexes: The structural characterization,
electrochemistry and catalytic activity
1
⇑
Shyamal Kumar Sarkar , Mahendra Sekhar Jana, Tapan Kumar Mondal, Chittaranjan Sinha
Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata 700032, India
a r t i c l e i n f o
a b s t r a c t
Trans-(I,I)-[MI2(CO)2(RaaiR0)] (M = Ru, Os) (RaaiR0 = 1-alkyl-2-(arylazo)imidazoles) complexes have been
synthesized by the reaction of RaaiR0 and [Ru(CO)4I2] or [Os(CO)4I2] in acetonitrile solution and the com-
plexes have been characterized by elemental analysis and spectral (FT-IR, UV–Vis, 1H NMR) data. The
structural confirmation has been determined by single crystal X-ray diffraction of trans-(I,I)-[MI2(CO)2
(HaaiEt)] (M = Ru, 3b; Os, 5b) (HaaiEt = 1-ethyl-2-(phenylazo)imidazole) and has shown a distorted octa-
hedral geometry with a trans-I,I and cis-CO, CO configuration. The complexes show a M(III)/M(II) couple
and the reduction of the chelated azoimine ligand. These complexes act as catalysts in the oxidation of
PhCH2OH to PhCHO, 2-butanol (C4H9OH) to 2-butanone, cyclopentanol (C5H9OH) to cyclopentanone
and cyclohexanol to cyclohexanone by N-methylmorpholine-N-oxide (NMO). The molecular orbital dia-
gram has been drawn by density functional theory (DFT) using the optimized geometry from the single
crystal X-ray parameters. The assignments of electronic spectra have been carried out by TD-DFT calcu-
lations both in the gas and acetonitrile phases.
Article history:
Received 30 July 2012
Accepted 5 November 2012
Available online 21 November 2012
Keywords:
Ruthenium and osmium CO-iodide
azoimidazoles
X-ray structures
Catalytic oxidation
Electrochemistry
DFT calculations
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
the use of M–I-carbonyl compounds as starting compounds to syn-
thesize polypyridine complexes are rare [37]. The chemical activity
The metal catalyzed oxidation of primary and secondary alco-
hols to the corresponding aldehydes and ketones, respectively
(Scheme 1), plays an important role in organic synthesis. Catalyses
using ruthenium complexes of different heterocyclic-N door li-
gands are an active area of present research [1–14]. The catalytic
efficiency of ruthenium(II)-carbonyl complexes has been studied
using oxidizing agents like H2O2, ButOOH and N-methylmorpho-
line-N-oxide (NMO) [15–18]. The catalytic efficiency of the os-
mium-carbonyl complexes are relatively less explored than the
ruthenium-carbonyl complexes. This may be due to lower catalytic
efficiency of osmium complexes because of relativistic effect of the
heavier Os(II) than Ru(II).
of the M–X function (X = halide or pseudohalide) is controlled by
the bond strength, the oxidation state of M and the electronic prop-
erties of M and X; iodide, being the least electronegative and a
highly polarizable halide, may be useful to catalyze different cou-
pling, cross-coupling and oxidation reactions [38]. The catalytic
efficiency of a molecule depends on the lability of bonds, chemical
oxidation or reduction of the species and the stability of the prod-
uct(s). In this work, we report the synthesis and characterization of
Ru(II)-/Os(II)-CO-diiodide complexes of 1-alkyl-2-(arylazo)imida-
zoles (RaaiR0). Single crystal X-ray diffraction studies have been
undertaken for structural confirmation of the complexes. The elec-
tronic structures of the complexes have been calculated by DFT and
the TD-DFT methods and have been used to interpret the electronic
spectra and redox properties. The catalytic activity of these com-
pounds is examined by the oxidation of primary and secondary
alcohols to aldehydes and ketones, respectively, using N-methyl-
morpholine-N-oxide (NMO).
Azopyridine complexes of ruthenium have been useful in many
catalytic reactions, such as hydroformylation, CO2 reduction, water
gas shift reaction [19–24], etc. We have designed 1-alkyl-2-(ary-
lazo)imidazoles (Scheme 2; HaaiR0, 1 and MeaaiR0, 2), a
p-acidic
chelating azoimine (–N@N–C@N–) ligand [25–29]. The Ru- and
Os-carbonyl complexes of these ligands containing M–Cl/M–H
bonds (M = Ru, Os) are reported in literature [30–36]. However,
2. Results and discussion
2.1. Synthesis and formulation
⇑
Corresponding author. Fax: +91 033 2413 7121.
E-mail address: c_r_sinha@yahoo.com (C. Sinha).
Present address: Department of Chemistry, Uluberia College, Uluberia, Howrah
1
[Ru(CO)4I2] and [Os(CO)4I2] were used as the starting metal
compounds and 1-alkyl-2-(arylazo)imidazoles (Scheme 2) were
711315, India.
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.11.013

S.K. Sarkar et al. / Polyhedron 50 (2013) 246–254
247
the ligands. A mixture of [M(CO)4I2] (M = Ru, Os) and the appropri-
ate RaaiR0 in acetonitrile under refluxing condition in a dinitrogen
atmosphere synthesized dark red solid products. The formulation
of the complexes, [MI2(CO)2(RaaiR0)] (M = Ru (3, 4); Os (5, 6) was
supported by microanalytical data. The stereochemical disposition
of the donor groups has been confirmed by single crystal X-ray dif-
fraction and shows the two CO ligands are in a cis-configuration
and the two Iꢀ ligands are bonded in trans positions, while RaaiR0
(Scheme 2) acts as an N(imidazole) and N(azo) chelator.
The complexes are diamagnetic, indicating the presence of the
metal in the +2 oxidation state (d6). The higher stability of the
trans-(I,I)-cis-(CO, CO) isomer relative to the cis-(I,I)-trans-(CO,
CO) isomer is not surprising due to the trans weakening effect of
CO.
2.2. Infrared and 1H NMR spectral studies
Fig. 1. ORTEP structure of [RuI2(CO)2(HaaiEt)] (3b) with 35% ellipsoidal probability.
The complexes 3–6 show a sharp stretch at 1993–2003 and
2047–2058 cmꢀ1, corresponding to
m(CO). The presence of two
m
(CO) stretches refer to a cis-M(CO)2 configuration [29]. Infrared
spectra of the complexes exhibit
m
m
(C@N) at 1556–1569 cmꢀ1 and
(N@N) at 1346–1360 cmꢀ1. The azo (–N@N–) stretching is signif-
icantly shifted to the lower frequency region compared to the free
ligand value (1400–1410 cmꢀ1), which supports efficient
d
p
(Ru) ? p⁄(N@N) donation in the complexes [25,31–34].
The 1H NMR spectra of the complexes have been recorded in
CDCl3 solution and the spectral data are given in Section 3. The
spectra were assigned on comparing the spectra of the free ligands,
Ru(II)-complexes [25,29] and Os(II)-complexes [35]. The imidazo-
lyl protons, 4- and 5-H, appear as a broad singlet at 7.75–7.85
and 7.45–7.55 ppm, respectively and have been downfield shifted
(Dd = 0.60–0.80 ppm). The singlet nature of the imidazolyl protons
may be due to rapid proton exchange on the NMR timescale with
solvent protons (may be coming from moisture during the mea-
surement). The 1-R signals of the chelated ligand appear as fol-
lows: 1-Me appears as a singlet at 4.25–4.30 ppm; 1-CH2-CH3
gives a quartet (4.55–4.70 ppm, J = 7.3 Hz) and a triplet (1.65–
1.70 ppm, J = 7.4 Hz) respectively; 1-CH2-(Ph) gives a singlet at
5.70–5.85 ppm. Aryl protons (7-H–11-H) appear at their usual po-
sition. The p-Me substituent (MeaaiR0) shows upper field shifting of
Fig. 2. ORTEP structure [OsI2(CO)2(HaaiEt)] (5b) with 35% ellipsoidal probability.
these protons due to an electron donating effect compared to the
phenyl group of HaaiR0.
2.3. Molecular structures
The X-ray structures of [RuI2(CO)2(HaaiEt)] (3b) and [OsI2(-
CO)2(HaaiEt)] (5b) are shown in Figs. 1 and 2, respectively; selected
bond parameters are listed in Table 1. The molecules consist of a
central Ru and Os atom surrounded by six coordination centers,
and the arrangements are distorted octahedral. The atomic
arrangements involve two trans-I, two cis-CO and a chelated 1-
ethyl-2-(phenylazo)imidazole (HaaiEt) ligand within the MI2C2N2
coordination spheres. The CO groups are located trans to the azo-
N (N0) and imidazole-N (N) coordination. The trans-I angle, I(1)–
Ru–I(2) and I(1)–Os–I(2) are 177.60(1) and 174.78(2), respectively,
and lie in the range of reported data [19,23–30]. The N(1)–Ru–N(7)
and N(1)–Os–N(7) chelate angles are 75.20(9)° (3b) and 74.60(2)°
(5b). Other angles about Ru and Os define the distorted octahedral
geometry.
Scheme 1. Catalytic oxidation of secondary alcohols to ketones by NMO.
4
5
5
4
I
M
I
CO
CO
N
N
N
N
R
R
N
N
N
N
7
11
10
7
8
11
10
8
9
9
R
R
The Ru(1)–N(7) and Os(1)–N(7) bond distances [N(7) is azo-N),
2.141(2) Å (3b) and 2.129(5) Å (5b)] are longer than the Ru(1)–
N(1) and Os(1)–N(1) bond distances [N(1) is imidazole-N,
2.095(2) Å (3b) and 2.090(5) Å (5b)] in complexes 3b and 5b. In
general, the Ru–N(azo) bond distance is shorter than the
RaaiR/
[MI2(CO)2(RaaiR/)]
R = H (1), Me (2); R/ = Me (a), Et (b) CH2Ph (c); M = Ru (3, 4) and Os (5, 6)
Scheme 2. The ligands and the complexes.

248
S.K. Sarkar et al. / Polyhedron 50 (2013) 246–254
Table 1
bonyl bonding in the complexes. The NBOs of C–O and M–C are
three and one, respectively. The Ru–C and the Os–C bond orbitals
are polarized towards the carbon atom, and the C–O bond orbitals
are polarized towards the oxygen. The occupancies and hybridiza-
tion of the C–O and M–C bonds are summarized in the Supplemen-
tary data (Table S1). The highly populated anti-bonding NBOs
(0.308–0.318 in 3b and 0.299–0.312 in 5b) indicate the higher ex-
Selected bond distances (Å) and bond angles (°) for [RuI2(CO)2(HaaiEt)] (3b) and
[OsI2(CO)2(HaaiEt)] (5b).
[RuI2(CO)2(HaaiEt)] (3b)
[OsI2(CO)2(HaaiEt)] (5b)
X-ray
DFT/B3LYP
X-ray
DFT/B3LYP
Bond distances (Å)
M(1)–I(1)
M(1)–I(2)
M(1)–N(1)
M(1)–N(7)
M(1)–C(16)
M(1)–C(17)
C(16)–O(1)
C(17)–O(2)
N(6)–N(7)
2.698(3)
2.791
2.788
2.117
2.182
1.891
1.894
1.150
1.151
1.283
2.711(8)
2.785
2.778
2.135
2.167
1.905
1.902
1.153
1.154
1.284
tent of d
in back donation decreases the C–O bond strength which means
lowering of (CO). It is indeed observed. The calculated electron
p
(M) ? p⁄(CO) (where M = Ru and Os) donation. Increase
2.699(2)
2.095(3)
2.141(2)
1.890(4)
1.887(4)
1.127(4)
1.135(4)
1.281(3)
2.705(9)
2.090(5)
2.129(5)
1.894(8)
1.856(8)
1.100(10)
1.155(10)
1.286(8)
m
populations on the 4d orbitals of Ru and 5d orbitals of Os are
7.60 and 7.42 for 3b and 5b, respectively. The NBO charge of the
Ru and Os atoms are ꢀ0.096 and +0.022 in 3b and 5b respectively.
The charge on the carbonyl carbon is positive (+0.672 in 3b and
+0.626 in 5b), while that on the oxygen atom is negative (ꢀ0.431
in 3b and ꢀ0.435 in 5b) (Supplementary data, Table S2).
Bond angles (°)
N(1)–M(1)–N(7)
N(1)–M(1)–C(16)
N(1)–M(1)–C(17)
N(1)–M(1)–I(1)
N(1)–M(1)–I(2)
N(7)–M(1)–C(16)
N(7)–M(1)–C(17)
N(7)–M(1)–I(1)
N(7)–M(1)–I(2)
C(16)–M(1)–C(17)
C(16)–M(1)–I(1)
C(16)–M(1)–I(2)
C(17)–M(1)–I(1)
C(17)–M(1)–I(2)
I(1)–M(1)–I(2)
75.21(9)
95.09(1)
175.41(1)
89.93(7)
89.35(7)
170.13(1)
100.68(1)
87.98(6)
89.63(6)
89.08(1)
90.26(9)
92.07(9)
91.99(9)
88.57(9)
177.60(5)
177.2(3)
178.1(3)
74.91
94.57
175.0
89.88
88.29
169.4
100.8
88.69
89.11
89.72
90.23
91.69
92.60
89.08
177.4
177.4
177.9
74.60(2)
98.50(3)
172.60(3)
88.15(2)
87.52(2)
173.00(2)
99.00(3)
89.82(15)
86.22(15)
87.9(3)
91.1(2)
92.4(2)
95.6(2)
88.4(2)
174.78(2)
179.1(7)
174.1(7)
74.01
95.82
172.9
88.79
87.72
169.7
99.05
90.64
87.65
91.06
90.57
90.53
92.62
90.73
176.4
177.0
179.3
Selected molecular orbitals, along with the energy and compo-
sition, of 3b and 5b have been summarized as Supplementary data
in Tables S3 and S4, respectively. The higher energy occupied orbi-
tals, HOMO and HOMOꢀ1, have 74–83% iodine p
with a small contribution from metal d-orbitals. HOMOꢀ2 to
and/or (HaaiEt) character. The
p character along
HOMOꢀ6 have either iodine p
p
p
metal d-orbital contribution (45–70%) has been found in HOMOꢀ7
to HOMOꢀ9 molecular orbitals. The LUMO of the complexes has
87–91% HaaiEt character. The azo function in HaaiEt contributes
48–50% to its composition. The HOMO–LUMO energy gap in the
complexes is 2.31 and 2.22 eV in 3b and 5b, respectively. LUMO+1
M(1)–C(16)–O(1)
M(1)–C(17)–O(2)
has mixed metal d
show a high mixing of metal d
p
and iodine p
p character. LUMO+2 and LUMO+3
p
and p⁄(CO) orbitals (Fig. 3 and Sup-
plementary materials Figs. S1 and S2).
Ru–N(imidazole) bond length [25,29–32]. The –N@N– bond length
is 1.283(3) and 1.286(6) Å in 3b and 5b, respectively which are
longer than the free ligand azo distance, 1.267(3) Å [39]. The elon-
gation of the azo bond in complexes is due to extensive
2.5. Electronic transitions and TD DFT calculations
The electronic absorption spectra were measured at room tem-
perature in acetonitrile, and the experimental absorption bands are
assigned using the singlet–singlet vertical excitations calculated by
the TD-DFT/CPCM method. Absorption spectra of the representa-
tive complexes 3b and 5b in acetonitrile are shown in Fig. 4. Some
of the calculated excitation wavelengths and their assignments are
given in Table 2 for 3b and 5b. A low energy weak band at 517 and
546 nm has been observed for 3b and 5b respectively, which cor-
dp
(Ru) ? p⁄(N@N) donation. The Ru–C bond lengths of 3b are
Ru(1)–C(16), 1.890(4), slightly longer, and Ru(1)–C(17),
1.887(4) Å which is slightly shorter than the Ru–C bond lengths
of trans-Cl,Cl-[Ru(CO)2Cl2(HaaiEt)] [23] ((Ru(1)–C(1), 1.879(3);
Ru(1)–C(2), 1.894(3) Å). The two Os–C bond lengths of 5b differ
significantly: Os(1)–C(16), 1.894(8); Os(1)–C(17), 1.856(8) Å. The
C–O distances (C(16)–O(1), 1.127(4) (3b) and 1.100(10) (5b);
C(17)–O(2), 1.135(4) (3b) and 1.155(10) (5b) Å) are different than
those of the previously reported data [23]. This may be due to
the effect of the Ru–I function where I delocalizes more charge
density than Cl in Ru–Cl of trans-Cl,Cl-[Ru(CO)2Cl2(HaaiEt)] [23].
The pendant phenyl ring is inclined to the mean plane of the che-
late ring by 24.57(12)° (3b) and 33.26(8)° (5b).
responds to d
sharp band at 405–420 nm in the complexes corresponds to mixed
(HaaiEt) ? p⁄(HaaiEt) and (I) ? p⁄(HaaiEt) charge transfer
transitions, while the moderately intense band at 280–310 nm is
p(M)/pp
(I) ? p⁄(HaaiEt) transitions. The intense
p
pp
from purely intra-ligand p
(HaaiEt) ? p⁄(HaaiEt) transitions.
DFT calculations on these two molecules were carried out and
the optimized geometries of these compounds agree well with
the experimentally determined metric parameters (Table 1). The
calculations show that the energy of the HOMO of trans-(I,I)-[RuI2
(CO)2(HaaiEt)] (3b) (E(HOMO): ꢀ5.79 eV) is lower than that of
cis-(I,I)-[RuI2(CO)2(HaaiEt)] (E(HOMO): ꢀ4.82 eV) and cis-(I)-cis-
(CO)-[RuI2(CO)2(HaaiEt)] (E(HOMO): ꢀ5.16 eV). Similarly, the
energy of the HOMO of trans-(I,I)-[OsI2(CO)2(HaaiEt)] (5b)
(E(HOMO): ꢀ5.74 eV) is lower than that of cis-(I,I)-[OsI2(CO)2
(HaaiEt)] (E(HOMO): ꢀ4.80 eV) and cis-(I)-cis-(CO)-[OsI2(CO)2
(HaaiEt)] (E(HOMO): ꢀ5.14 eV). This reflects the better stability
of the trans-(I,I) than cis-(I,I) configuration, which may be the rea-
son for the isolation of trans-(I,I)-[MI2(CO)2(RaaiR0)]. The structural
agreement between theory and experiment is satisfactory (Table 1).
2.6. Electrochemistry
The complexes 3–6 show one quasi-reversible, 1.44–1.49 V (DE,
110–120 mV), and one irreversible, 0.63–0.67 V, oxidative re-
sponse positive to the reference Ag/AgCl electrode, along with
one reversible reductive response, ꢀ(0.52–0.56) V
(DE, 84–
90 mV), and one irreversible, ꢀ(1.34–1.45) V, cathodic peak when
scanned in the negative potential range (Fig. 5 and Table 3).
The redox couples have been assigned on the basis of the DFT
results. The HOMO and HOMOꢀ1 of 3b has 15–18% Ru character
and 80–83% iodine contribution, whereas 5b has 17–22% Os char-
acter and 74–79% iodine contribution. So, the first irreversible oxi-
dation of the cyclic voltammogram of the complexes 3–6 has been
assigned to the Iꢀ/½I2 oxidation and the quasi-reversible second
oxidation at higher potential range is the M(II)/M(III) couple. The
LUMOs of the complexes exclusively have ligand character with
47–50% azo contribution; so the reductions are taking place on
the azo function in all the complexes, leading to the formation of
2.4. DFT calculations and NBO analyses
Natural bond orbital analyses of 3b and 5b have been carried
out on the DFT optimized geometry to understand the metal car-
ꢀꢀ
2ꢀ
the radical anion (RaaiR0 ) and RaaiR0
.

S.K. Sarkar et al. / Polyhedron 50 (2013) 246–254
249
Fig. 3. Contour plots of some selected molecular orbitals of [RuI2(CO)2(HaaiEt)] (3b) and [OsI2(CO)2(HaaiEt)] (5b).
immediately analyzed by GC. The aldehyde or ketone formed after
2 h of reflux was determined by GC and there was no detectable oxi-
dation in the absence of the ruthenium complex. The results of the
investigation suggest that the complexes are able to react efficiently
with NMO to yield a high valent ruthenium/osmium-oxo species
[10–15], which is capable of oxygen atom transfer to the alcohols.
The oxidation ability of cyclopentanol and cyclohexanol are better
than benzyl alcohol and 2-butanol. The residue obtained by evapora-
tion of the resultant solution to dryness, had shown a band at 861
and 820 cmꢀ1, characteristic of Ru(IV)@O and Os(IV)@O species,
respectively. The catalytic efficiency of [RuI2(CO)2(RaaiR0)] is higher
than that of [OsI2(CO)2(RaaiR0)], which can be explained in terms of
the relativistic effects of the 4d and 5d orbitals [40], the M–CO bond
energies and the stability of the M(IV)@O intermediates. Because of a
relativistic effect, the 5d orbital of osmium becomes larger in size;
hence the interelectronic repulsion in this orbital is reduced, unlike
the 4d orbital of ruthenium. The oxidized catalyst M(IV)@O may be
more stable in the case of osmium compared to ruthenium and the
rate of alcohol oxidation using 3b as the catalyst could be more
favorable than that using 5b. The 5d orbitals of Os (5b) are not suffi-
ciently stabilized, compared to the 4d orbitals of Ru in 3b (EHOMO (Os-
complex, 5b), ꢀ5.74 eV and EHOMO (Ru-complex, 3b), ꢀ5.79 eV).
The role of the M–X (X = Cl, I) function to control the catalytic effi-
ciency of [MI2(CO)2(RaaiR0)] has been examined with reference to
ruthenium complexes and the results are compared with [RuCl2(-
CO)2(HaaiMe/HaaiEt)] (Table 4). It is calculated that the rate of oxida-
tion of PhCH2OH ? PhCHO is higher for the reaction with
[RuCl2(CO)2(HaaiR0)] compared to [RuI2(CO)2(HaaiR0)]. These two
complexes have only difference of the Ru–Cl versus Ru–I bonds.
The Ru–I bond (bond distances 2.698(3) and 2.699(2) Å) is longer
than Ru–Cl (2.3798(8) and 2.3852(9) Å) [23] so we may apprehend
a better lability of the Ru–I bonds. Because of the higher electropos-
itive character of iodide than chloride, the oxidant may be consumed
by iodide for some self oxidation reaction and this may be responsi-
ble for the low percentage conversion.
Fig. 4. UV–Vis spectra of [RuI2(CO)2(HaaiEt)] (3b) (—) and [OsI2(CO)2(HaaiEt)] (5b)
(ꢁꢁꢁꢁꢁ) in acetonitrile.
2.7. Catalytic oxidation of alcohols
Primary and secondary alcohols are oxidized to aldehydes and
ketones, respectively, and these reactions have been studied in
the presence of NMO as an oxidant in the presence of [MI2(CO)2(-
RaaiR0]. A typical reaction using the ruthenium and osmium com-
plexes as catalysts and benzyl alcohol, 2-butanol, cyclopentanol
and cyclohexanol as substrates at a 1:100 molar ratio is detailed
in Section 3 (see below). The reaction has been carried out in CH2Cl2
under refluxing conditions for an appropriate period of time. The
complexes catalyze the oxidation of PhCH2OH to PhCHO, C4H9OH
to C4H7O (2-butanone), C5H9OH to C5H8O (cyclopentanone) and
CyCH-OH to CyC@O (cyclohexanone) with high yields. The ether ex-
tracts were evaporated to give the aldehydes/ketones, which were

250
S.K. Sarkar et al. / Polyhedron 50 (2013) 246–254
Table 2
Calculated singlet–singlet vertical electronic transitions for [RuI2(CO)2(HaaiEt)] (3b) and [OsI2(CO)2(HaaiEt)] (5b).
Excited state
Energy (eV)
ktheo
f
Key transitions
Character
[RuI2(CO)2(HaaiEt)] (3b)
1
2
3
7
8
13
17
1.940
2.024
2.366
2.855
3.029
3.615
3.819
638.9
612.6
523.9
434.1
409.3
342.9
324.5
0.0033
0.0077
0.0030
0.3551
0.1446
0.0654
0.0516
(97%)HOMO ? LUMO
Ru(d
p
p
)/I(p
)/I(p
p
p
) ? HaaiEt(p⁄
) ? HaaiEt(p⁄
)
)
(96%)HOMOꢀ1 ? LUMO
(93%)HOMOꢀ2 ? LUMO
(64%)HOMOꢀ4 ? LUMO
(72%)HOMOꢀ5 ? LUMO
(76%)HOMOꢀ6 ? LUMO
(72%)HOMOꢀ10 ? LUMO
Ru(d
I(p
p
) ? HaaiEt(p⁄
)
HaaiEt(
HaaiEt(
HaaiEt(
HaaiEt(
p
p
p
p
)/I(p
)/I(p
p
p
) ? HaaiEt(p⁄
)
)
) ? HaaiEt(p⁄
) ? HaaiEt(p⁄
) ? HaaiEt(p⁄
)
)
[OsI2(CO)2(HaaiEt)] (5b)
1
2
3
5
9
11
12
1.8157
1.9893
2.4795
2.9589
3.2396
3.5311
3.7750
682.8
623.3
500.0
419.0
382.7
351.1
328.4
0.0016
0.0230
0.0035
0.3640
0.1367
0.0672
0.0601
(95%)HOMO ? LUMO
Os(d
p
p
)/I(p
)/I(p
p
p
) ? HaaiEt(p⁄
) ? HaaiEt(p⁄
)
)
(92%)HOMOꢀ1 ? LUMO
(93%)HOMOꢀ2 ? LUMO
(72%)HOMOꢀ4 ? LUMO
(78%)HOMOꢀ5 ? LUMO
(73%)HOMOꢀ6 ? LUMO
(74%)HOMOꢀ11 ? LUMO
Os(d
I(p
HaaiEt(
I(p
p
) ? HaaiEt(p⁄
)
p
) ? HaaiEt(p⁄
)
p
) ? HaaiEt(p⁄
)
HaaiEt(
HaaiEt(
p
p
) ? HaaiEt(p⁄
) ? HaaiEt(p⁄
)
)
Fig. 5. Cyclic voltammogram of [RuI2(CO)2(HaaiEt)] (3b) (—) and [OsI2(CO)2(HaaiEt)] (5b) (–ꢂ–) in acetonitrile solution, supporting electrolyte Bu4NClO4 (0.1 M), reference
electrode Ag/AgCl at a scan rate of 50 mV sꢀ1
.
Table 3
Cyclic voltammetric data of [MI2(CO)2(RaaiR0)] (3–6).
Complex
Cyclic voltammetrya
ꢀꢀ
2ꢀ c
E (Iꢀ/½I2)b (V)
E1/2 (MII/MIII) (V)
Ep, mV)
E1/2 (RaaiR0/RaaiR0ꢀꢀ) (V)
Ep, mV)
E (RaaiR0 /RaaiR0
) (V)
(
D
(D
3a
3b
3c
4a
4b
4c
5a
5b
5c
6a
6b
6c
0.652
0.641
0.652
0.665
0.647
0.657
0.634
0.634
0.637
0.632
0.641
0.637
1.477(110)
1.488(112)
1.481(110)
1.462(115)
1.457(110)
1.459(114)
1.445(110)
1.442(115)
1.437(110)
1.414(115)
1.424(120)
1.417(110)
ꢀ0.548(87)
ꢀ0.552(90)
ꢀ0.562(95)
ꢀ0.561(85)
ꢀ0.549(85)
ꢀ0.550(90)
ꢀ0.518(85)
ꢀ0.507(85)
ꢀ0.516(90)
ꢀ0.534(84)
ꢀ0.537(86)
ꢀ0.531(90)
ꢀ1.417
ꢀ1.423
ꢀ1.431
ꢀ1.424
ꢀ1.442
ꢀ1.450
ꢀ1.354
ꢀ1.346
ꢀ1.351
ꢀ1.344
ꢀ1.339
ꢀ1.352
a
In acetonitrile solution, supporting electrolyte [Bu4N](ClO4) (0.1 M), reference electrode Ag/AgCl, scan rate = 50 mV sꢀ1. E = 0.5(Epa + Epc) where Epa and Epc are the anodic
½
and cathodic peak potentials, respectively;
D
Ep = Epa ꢀ Epc
.
b
Anodic potential.
c
Cathodic potential.

S.K. Sarkar et al. / Polyhedron 50 (2013) 246–254
251
Table 4
Catalytic oxidation of alcohols by [MI2(CO)2(RaaiR0)] (M = Ru(II) (3, 4) and Os(II) (5, 6) using NMO as the co-oxidant.
Complex
Substrate
Product
Yielda (%)
Turnoverb (%)
3a
benzyl alcohol
2-butanol
cyclopentanol
cyclohexanol
benzaldehyde
2-butanone
cyclopentanone
cyclohexanon
68
73
80
82
68
73
80
82
3b
benzyl alcohol
2-butanol
cyclopentanol
cyclohexanol
benzaldehyde
2-butanone
cyclopentanone
cyclohexanon
70
72
81
83
70
72
81
83
3c
benzyl alcohol
2-butanol
cyclopentanol
cyclohexanol
benzaldehyde
2-butanone
cyclopentanone
cyclohexanon
69
73
80
84
69
73
80
84
4a
benzyl alcohol
2-butanol
cyclopentanol
cyclohexanol
benzaldehyde
2-butanone
cyclopentanone
cyclohexanon
67
71
76
81
67
71
76
81
4b
benzyl alcohol
2-butanol
cyclopentanol
cyclohexanol
benzaldehyde
2-butanone
cyclopentanone
cyclohexanon
66
74
78
82
66
74
78
82
4c
benzyl alcohol
2-butanol
cyclopentanol
cyclohexanol
benzaldehyde
2-butanone
cyclopentanone
cyclohexanon
67
79
81
84
67
79
81
84
5a
benzyl alcohol
2-butanol
cyclopentanol
cyclohexanol
benzaldehyde
2-butanone
cyclopentanone
cyclohexanon
54
59
63
65
54
59
63
65
5b
benzyl alcohol
2-butanol
cyclopentanol
cyclohexanol
benzaldehyde
2-butanone
cyclopentanone
cyclohexanon
51
58
65
66
51
58
65
66
5c
benzyl alcohol
2-butanol
cyclopentanol
cyclohexanol
benzaldehyde
2-butanone
cyclopentanone
cyclohexanon
55
61
64
67
55
61
64
67
6a
benzyl alcohol
2-butanol
cyclopentanol
cyclohexanol
benzaldehyde
2-butanone
cyclopentanone
cyclohexanon
53
60
65
66
53
60
65
66
6b
benzyl alcohol
2-butanol
cyclopentanol
cyclohexanol
benzaldehyde
2-butanone
cyclopentanone
cyclohexanon
51
60
65
66
51
60
65
66
6c
benzyl alcohol
2-butanol
cyclopentanol
cyclohexanol
benzaldehyde
2-butanone
cyclopentanone
cyclohexanon
53
61
63
66
53
61
63
66
[RuCl2(CO)2(HaaiMe)]
[RuCl2(CO)2(HaaiEt)]
benzyl alcohol
2-butanol
cyclopentanol
cyclohexanol
benzaldehyde
2-butanone
cyclopentanone
cyclohexanon
84
90
92
96
84
90
92
96
benzyl alcohol
2-butanol
cyclopentanol
cyclohexanol
benzaldehyde
2-butanone
cyclopentanone
cyclohexanon
86
88
94
96
86
88
94
96
Substrate (1 mmol); NMO (3 mmol); complex (0.01 mmol); solvent dichloromethane.
a
The yield of product was determined using an Agilent 7890 series Gas chromatography instrument equipped with a flame ionization detector (FID) using a HP-5 column
of 30 m length, 0.53 mm diameter and 5.00
lm film thickness.
b
Moles of product per mole of catalyst.
prepared by a reported method [37]. 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 [n-Bu4N][ClO4] for the elec-
trochemical work were done as reported before [29]. Dinitrogen
was purified by bubbling through an alkaline pyrogallol solution.
All other chemicals and solvents were of reagent grade and were
3. Experimental
3.1. Materials and instrumentation
1-Alkyl-2-(phenylazo)imidazole (1) and 1-alkyl-2-(p-toly-
lazo)imidazole (2) were synthesized following a previously pub-
lished procedure [25]. [Ru(CO)4I2] and [Os(CO)4I2] were also

252
S.K. Sarkar et al. / Polyhedron 50 (2013) 246–254
used without further purification. Commercially available SRL silica
gel (60–120 mesh) was used for the column chromatography.
Microanalytical data (C, H, N) were collected on a Perkin-Elmer
2400 CHNS/O elemental analyzer. Infrared spectra were taken on a
RX-1 Perkin Elmer spectrophotometer with the samples prepared
as KBr pellets. UV–Vis spectral studies were performed on a Perkin
Elmer Lambda 25 spectrophotometer. 1H NMR spectra were re-
corded using a Bruker (AC) 300 MHz FTNMR spectrometer in
CDCl3. Cyclic voltammetric measurements were carried out using
a CH1 Electrochemical workstation. A platinum wire working elec-
trode, a platinum wire auxiliary electrode and Ag/AgCl reference
electrode were used in a standard three-electrode configuration.
[nBu4N][ClO4] was used as the supporting electrolyte in acetoni-
trile and the scan rate used was 50 mV sꢀ1 in acetonitrile under a
dinitrogen atmosphere. The reported potentials are uncorrected
for junction potentials.
314 (11548), 415 (14952), 509 (1715). Calc. for [RuI2(CO)2(Meaa-
iCH2Ph)], C19H16N4O2I2Ru (4c): C, 32.11; H, 2.09; N, 8.32. Found:
C, 31.92; H, 2.12; N, 5.31%. IR data (KBr disc) (cmꢀ1):
2054; m(C@N) 1556; m
m
(CO) 2002,
(N@N) 1352. 1H NMR data in CDCl3 (ppm):
7.78 (4-H, bs), 7.45 (5-H, bs), 5.53 (N-CH2-Ph, s), 7.89 (7, 11-H, d,
J = 8.0 Hz), 7.37 (8, 10-H, d, J = 8.0 Hz), 2.49 (9-CH3, s). UV–Vis (CH3-
CN) kmax (e
, Mꢀ1 cmꢀ1): 310 (13452), 412 (14925), 512 (1625).
3.2.2. Synthesis of [Os(CO)2I2(HaaiEt)] (5b)
Complex 5b was prepared by the reaction of [Os(CO)4I2]
(100 mg, 0.18 mmol) with HaaiEt (1b) (36.02 mg, 0.19 mmol) fol-
lowing the same procedure as for 3b. Yield was 90.67 mg (72%).
Compounds 5a, 5c, 6a, 6b and 6c were also synthesized following
the same procedure by the reaction of Os(CO)4I2 with 1a, 1c, 2a, 2b
and 2c respectively in the same molar ratio (1:1). The yields were
about (64–73)%.
Microanalytical data: Calc. for [OsI2(CO)2(HaaiMe)], C12H10N4-
O2I2Os (5a): C, 21.08; H, 1.47; N, 8.17. Found: C, 21.12; H, 1.46;
3.2. Synthesis of the complexes
N, 8.18%. IR data (KBr disc) (cmꢀ1):
m
(CO) 1999, 2051;
(N@N) 1353. 1H NMR data in CDCl3 (ppm): 7.72 (4-H, bs),
7.48 (5-H, bs), 4.30 (N-CH3, s), 8.06 (7, 11-H, d, J = 7.0 Hz), 7.63
(8-10-H, m). UV–Vis (CH3CN) kmax
, Mꢀ1 cmꢀ1): 287 (21456),
m(C@N)
3.2.1. Synthesis of [Ru(CO)2I2(HaaiEt)] (3b)
1561; m
To 20 ml acetonitrile suspension of [Ru(CO)4I2] (100 mg,
0.21 mmol), a 15 ml acetonitrile solution of HaaiEt (1b) (45 mg,
0.23 mmol) was added in a 1:1 molar ratio and the solution was re-
fluxed for 4 h under a N2 atmosphere. The color of the solution
changed from red to dark red. The solvent was removed under re-
duced pressure using a rota-evaporator. The dark red dry mass was
then dissolved in a minimum volume of CH2Cl2 and subjected to
chromatographic separation on a silica gel column (60–120 mesh).
The red solution was eluted by acetonitrile-benzene (1:9, v/v).
Evaporation of the solvent under reduced pressure afforded pure
complex 3b. The yield was 97 mg (74%). The compounds 3a, 3c,
4b, 4b and 4c were also synthesized following the same procedure
by the reaction of [Ru(CO)4I2] with 1a, 1c, 2a, 2b and 2c respec-
tively under identical reaction conditions. The yields were 66–75%.
Microanalytical data: Calc. for [RuI2(CO)2(HaaiMe)], C12H10N4-
O2I2Ru (3a): C, 24.17; H, 1.69; N, 9.39. Found: C, 24.25; H, 1.63;
(e
415 (25465), 542 (2945). For [OsI2(CO)2(HaaiEt)], C13H12N4O2I2Os
(5b): C, 22.30 (22.28); H, 1.73 (1.74); N, 8.00 (7.99). IR data (KBr
disc) (cmꢀ1): (N@N) 1348. 1H
m(CO) 1996, 2050; m(C@N) 1569; m
NMR data in CDCl3 (ppm): 7.69 (4-H, bs), 7.50 (5-H, bs), 4.66
(N-CH2-CH3, q, J = 7.0 Hz), 1.70 (N-CH2-CH3, t, J = 7.0 Hz), 8.00 (7,
11-H, d, J = 7.0 Hz), 7.61 (8-10-H, m). UV–Vis (CH3CN) kmax
(e
, Mꢀ1 cmꢀ1): 280 (22546), 413 (27401), 546 (3131). Calc. for
[OsI2(CO)2(HaaiCH2Ph)], C18H12N4O2I2Os (5c): C, 27.29; H, 1.62;
N, 7.49. Found: C, 27.18; H, 1.62; N, 7.51%. IR data (KBr disc)
(cmꢀ1): (N@N) 1352. 1H NMR
m(CO) 2001, 2048; m(C@N) 1563; m
data in CDCl3 (ppm): 7.70 (4-H, bs), 7.51 (5-H, bs), 5.57 (N-CH2-
Ph, s), 8.03 (7, 11-H, d, J = 7.0 Hz), 7.62 (8-10-H, m). UV–Vis (CH3-
CN) kmax (e
, Mꢀ1 cmꢀ1): 290 (23452), 410 (26125), 540 (2745).
Calc. for [OsI2(CO)2(MeaaiMe)], C13H12N4O2I2Os (6a): C, 22.30; H,
N, 9.35%. IR data (KBr disc) (cmꢀ1):
1563;
(N@N) 1349. 1H NMR data in CDCl3 (ppm): 7.78 (4-H, s),
7.43 (5-H, bs), 4.27 (N-CH3, bs), 8.04 (7, 11-H, d, J = 8.0 Hz), 7.60
(8-10-H, m). UV–Vis (CH3CN) kmax
, Mꢀ1 cmꢀ1): 310 (13906),
m
(CO) 1993, 2047;
m
(C@N)
1.73; N, 8.01. Found: C, 22.29; H, 1.74; N, 8.16%. IR data (KBr disc)
m
(cmꢀ1): (N@N) 1360. 1H NMR
m(CO) 2002, 2051; m(C@N) 1562; m
data in CDCl3 (ppm): 7.68 (4-H, bs), 7.47 (5-H, bs), 4.32 (N-CH3,
(
e
s), 7.95 (7, 11-H, d, J = 7.0 Hz), 7.41 (8,10-H, d, J = 8.5), 2.47 (9-
406 (15651), 516 (1602). Calc. for [RuI2(CO)2(HaaiEt)], C13H12N4O2-
CH3, s). UV–Vis (CH3CN) kmax (e
, Mꢀ1 cmꢀ1): 295 (19457), 418
I2Ru (3b): C, 23.62; H, 1.98; N, 9.18. Found: C, 23.70; H, 1.89; N,
(25134), 537 (2947). Calc. for [OsI2(CO)2(MeaaiEt)], C14H14N4O2I2-
9.20%. IR data (KBr disc) (cmꢀ1):
m
(CO) 1999, 2058;
m
(C@N) 1561;
Os (6b): C, 23.54; H, 1.98; N, 7.84. Found: C, 23.49; H, 1.96; N,
m
(N@N) 1346. 1H NMR data in CDCl3 (ppm): 7.79 (4-H, bs), 7.47
7.73%. IR data (KBr disc) (cmꢀ1):
m
m
(CO) 2003, 2049;
m(C@N) 1560;
(5-H, bs), 4.64 (N-CH2-CH3, q, J = 7.0 Hz), 1.68 (N-CH2-CH3, t,
(N@N) 1353. 1H NMR data in CDCl3 (ppm): 7.67 (4-H, bs), 7.45
J = 7.0 Hz), 8.04 (7, 11-H, d, J = 7.0 Hz), 7.59 (8-10-H, m). UV–Vis
(5-H, bs), 4.63 (N-CH2-CH3, q, J = 7.0 Hz), 1.67 (N-CH2-CH3, t,
J = 8.0 Hz), 7.93 (7, 11-H, d, J = 7.0 Hz), 7.43 (8, 10-H, d,
(CH3CN) kmax (e
, Mꢀ1 cmꢀ1): 313 (14292), 405 (16449), 517
(1473). Calc. for [RuI2(CO)2(HaaiCH2Ph)], C18H14N4O2I2Ru (3c): C,
J = 9.0 Hz), 2.46 (9-CH3, s). UV–Vis (CH3CN) kmax (e
, Mꢀ1 cmꢀ1):
31.01; H, 1.84; N, 8.51. Found: C, 31.07; H, 1.79; N, 8.52%. IR data
287 (21484), 415 (28451), 540 (2871). Calc. for [OsI2(CO)2(Meaa-
(KBr disc) (cmꢀ1):
m
(CO) 2001, 2049;
m
(C@N) 1558;
m
(N@N) 1351.
iCH2Ph)], C19H16N4O2I2Os (6c): C, 28.36; H, 1.85; N, 7.35. Found:
1H NMR data in CDCl3 (ppm): 7.81 (4-H, bs), 7.48 (5-H, bs), 5.62
C, 28.34; H, 1.84; N, 7.41%. IR data (KBr disc) (cmꢀ1):
2051; m(C@N) 1559; m
m
(CO) 2000,
(N-CH2-Ph, s), 8.08 (7, 11-H, d, J = 7.0 Hz), 7.57 (8-10-H, m). UV–
(N@N) 1356. 1H NMR data in CDCl3 (ppm):
Vis (CH3CN) kmax
(
e
, Mꢀ1 cmꢀ1): 305 (14254), 408 (15651), 520
7.70 (4-H, bs), 7.48 (5-H, bs), 5.55 (N-CH2-Ph, s), 7.97 (7, 11-H, d,
(1578). Calc. for [RuI2(CO)2(MeaaiMe)], C13H12N4O2I2Ru (4a): C,
J = 7.0 Hz), 7.39 (8, 10-H, d, J = 9.0 Hz), 2.45 (9-CH3, s). UV–Vis (CH3-
25.58; H, 1.98; N, 9.18. Found: C, 25.62; H, 1.99; N, 9.21%. IR data
CN) kmax (e
, Mꢀ1 cmꢀ1): 290 (22154), 412 (27346), 541 (3102).
(KBr disc) (cmꢀ1):
m(CO) 2003, 2053; m(C@N) 1562; m(N@N) 1360.
1H NMR data in CDCl3 (ppm): 7.76 (4-H, bs), 7.34 (5-H, bs), 4.25
3.3. X-ray crystal structure analysis
(N-CH3, s), 7.95 (7, 11-H, d, J = 8.0 Hz), 7.38 (8,10-H, d, J = 9.0 Hz),
2.48 (9-CH3, s). UV–Vis (CH3CN) kmax
415 (19005), 511 (1702). Calc. for [RuI2(CO)2(MeaaiEt)], C14H14N4-
(
e
, Mꢀ1 cmꢀ1): 314 (14738),
Details of the crystal analyses, data collection and structure
refinement data are given in Table 5. Crystal mounting was done
on glass fibers with epoxy cement. Single crystal data collections
were performed with an automated Bruker SMART APEX CCD dif-
fractometer. Unit cell parameters were determined from least-
O2I2Ru (4b): C, 26.93; H, 2.16; N, 8.97. Found: C, 26.88; H, 2.19; N,
8.92%. IR data (KBr disc) (cmꢀ1):
m
m
(CO) 2000, 2052;
m(C@N) 1559;
(N@N) 1357. 1H NMR data in CDCl3 (ppm): 7.75 (4-H, bs), 7.43
(5-H, bs), 4.62 (N-CH2-CH3, q, J = 7.0 Hz), 4.67 (N-CH2-CH3, t,
squares refinement of setting angles with h in the range
J = 8.0 Hz), 7.95 (7, 11-H, d, J = 8.0 Hz), 7.35 (8, 10-H, d,
2.40 6 h 6 25.35° (3b) and 1.97 6 h 6 25.98° (5b). Out of 11177
collected data 3211, number of refined parameters 200, for 3b
J = 8.0 Hz), 2.48 (9-CH3, s). UV–Vis (CH3CN): kmax (e
, Mꢀ1 cmꢀ1):

S.K. Sarkar et al. / Polyhedron 50 (2013) 246–254
253
Table 5
tional and the Lee–Yang–Parr non-local correlation functional [44–
46] (B3LYP) were used throughout. The 6-31G(d) basis set was
used for the C, H, N and O atoms, while the 6-311G(d) basis func-
tions was used for the I atoms [47]. The Lanl2TZ(f) basis set with
effective core potentials was employed for the Ru and Os atoms
[48]. The vibrational frequency calculations were performed to en-
sure that the optimized geometries represent the local minima and
there are only positive eigen values. Natural bond orbital analyses
were performed using the NBO 3.1 module of GAUSSIAN03 [49]. Ver-
tical electronic excitations based on B3LYP optimized geometries
were computed for the time-dependent density functional theory
(TD-DFT) formalism [50–52] in acetonitrile using a conductor-like
polarizable continuum model (CPCM) [50–52]. Gauss Sum [53] was
used to calculate the fractional contributions of various groups to
each molecular orbital.
Crystal data and details of the structure determination of [RuI2(CO)2(HaaiEt)] (3b) and
[OsI2(CO)2(HaaiEt)] (5b).
Compound
[RuI2(CO)2(HaaiEt)]
(3b)
[OsI2(CO)2(HaaiEt)]
(5b)
Formula
Mr
Crystal system
Space group
a (Å)
b (Å)
c (Å)
C
13H12N4O2l2Ru
C13H12N4O2I2Os
700.30
monoclinic
P21/n
8.283(5)
14.348(5)
15.098(5)
15.098(5)
1774.4(14)
4
10.676
293(2)
2.622
1.97–25.98
3414/0/199
611.14
monoclinic
P21/c
11.7935(14)
10.6119(10)
14.7790(16)
106.318(3)
1775.1(3)
4
4.372
93(2)
2.287
2.40–25.35
3211/0/200
b (°)
Cell volume (Å3)
Z
l
(mmꢀ1
)
T (K)
qcalcd (g cmꢀ3
h range (°)
)
Data/restraints/
4. Conclusion
parameters
R1a, wR2 [I > 2
r
(I)]
0.0246, 0.0409
1.07
0.0370, 0.0892
1.03
b
The reaction of 1-alkyl-2-(phenylazo)imidazole (HaaiR0) (1) and
1-alkyl-2-(p-tolylazo)-imidazole (MeaaiR0) (2) with [Ru(CO)4I2]
and [Os(CO)4I2] have isolated the complexes [MI2(CO)2I2(RaaiR0)]
in which RaaiR0 serve as an N(imidazole), N(azo) bidentate chela-
tor. Single crystal X-ray diffraction has confirmed the structures
of the complexes. Cyclic voltammetry shows the M(III)/M(II) redox
response, along with ligand reductions. The catalytic activity of the
complexes has been examined for the oxidation of benzyl alcohol
to aldehyde, 2-butanol to 2-butanone, cyclopentanol to cyclo-
pentanone and cyclohexanol to cyclohexanone using NMO as an
oxidant. DFT calculations have been used to explain the spectra
and redox properties of the complexes.
GOF
a
R =
wR = [
R
|F0 ꢀ Fc|/
RF0.
b
2
4 1/2
R
w(F0 ꢀ Fc2)/
R
wF0
]
are general but
w
are different, w = 1/
[r r
2(F2) + (0.0156P)2] for 3b; w = 1/[ 2(F2)+(0.0537P)2 + 1.1520P] for 5b, where
P = (F02 + 2Fc2)/3.
and 25112 collected data 3414, number of refined parameters 199,
for 5b with I > 2 (I) were used for the structure solution. The hkl
r
ranges are ꢀ19 6 h 6 14, ꢀ10 6 k 6 12, ꢀ17 6 l 6 17 for 3b and
ꢀ10 6 h 6 10, ꢀ17 6 k 6 17, ꢀ18 6 l 6 18 for 5b. Reflection data
were recorded using the
x scan technique. The structures were
solved and refined by the full-matrix least-squares techniques on
F2 using the SHELX-97 program [41,42]. The absorption corrections
were done by the multi-scan technique. All data were corrected
for Lorentz and polarization effects, and the non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were constrained
to ride on the respective carbon atoms with isotropic displacement
parameters equal to 1.2 times the equivalent isotropic displace-
ment of their parent atom in all cases.
Acknowledgments
Financial support from the Department of Science & Technology
and University Grants Commission, New Delhi are gratefully
acknowledged.
Appendix A. Supplementary data
3.4. Procedure for catalytic oxidation
CCDC 856090 and 804818 contain the supplementary crystallo-
graphic data for 3b and 5b, respectively. These data can be ob-
tained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-
033; or e-mail: deposit@ccdc.cam.ac.uk.
Catalytic oxidation of primary and secondary alcohols to the
corresponding aldehydes and ketones respectively by ruthe-
nium(II) and osmium(II) carbonyl iodide complexes were studied
in the presence of NMO as a co-oxidant and the byproduct, water,
was removed by using about 0.5 g of molecular sieves. Typical
reactions were carried out using the ruthenium and osmium com-
plexes as the catalyst and benzyl alcohol, 2-butanol, cyclopentanol
and cyclohexanol as substrates in a 1:100 molar ratio. Solutions of
the ruthenium and osmium complexes (0.01 mmol) in 20 cm3 CH2-
Cl2 were added to a solution of the substrate (1 mmol) and NMO
(3 mmol). The solution mixture was refluxed for 2 h and the sol-
vent was then evaporated from the mother liquor under reduced
pressure. The residue was then extracted with petroleum ether
(20 cm3) and was analyzed by GC using an Agilent 7890 series
Gas chromatography instrument equipped with a flame ionization
detector (FID) using a HP-5 column of 30 m length, 0.53 mm diam-
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