Osmium-hydride-carbonyl complex with thioether containing Schiff base ligand: Synthesis, crystal structure, electrochemistry and catalytic transfer hydrogenation

Article abstract of DOI:10.1016/j.jorganchem.2017.06.020

A new osmium(II) carbonyl complex, [Os(H)(CO)(PPh₃)₂(L)] (1) with thioether containg NNS donor ligand (where L = 2-(ethylthio)-N-((pyridine-2-yl)methylene))benzenamine) is synthesized and characterized by various spectroscopic techniques. The distorted octahedral environment around osmium in the complex is confirmed by single crystal X-ray structure. Cyclic voltammogram in acetonitrile exhibits Os(II)/Os(III) oxidation and ligand based reduction. The complex effectively catalyzed the transfer hydrogenation reaction of ketones in high yields in i-PrOH. The electronic structure and redox properties are interpreted by DFT studies.

Full text of DOI:10.1016/j.jorganchem.2017.06.020

Accepted Manuscript
Osmium-hydride-carbonyl complex with thioether containing Schiff base ligand:
Synthesis, crystal structure, electrochemistry and catalytic transfer hydrogenation
Sujan Biswas, Puspendu Roy, Subrata Jana, Tapan Kumar Mondal
PII:
S0022-328X(17)30415-1
10.1016/j.jorganchem.2017.06.020
JOM 20007
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 14 April 2017
Revised Date: 16 June 2017
Accepted Date: 22 June 2017
Please cite this article as: S. Biswas, P. Roy, S. Jana, T.K. Mondal, Osmium-hydride-carbonyl
complex with thioether containing Schiff base ligand: Synthesis, crystal structure, electrochemistry
and catalytic transfer hydrogenation, Journal of Organometallic Chemistry (2017), doi: 10.1016/
j.jorganchem.2017.06.020.
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GRAPHICAL ABSTRACT

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Osmium-hydride-carbonyl complex with thioether containing Schiff base
ligand: Synthesis, crystal structure, electrochemistry and catalytic transfer
hydrogenation
Sujan Biswas, Puspendu Roy, Subrata Jana and Tapan Kumar Mondal*
Inorganic Chemistry Section, Department of Chemistry, Jadavpur University, Kolkata-700032,
India.
Abstract
A new osmium(II) carbonyl complex, [Os(H)(CO)(PPh3)2(L)] (1) with thioether containg NNS
donor ligand (where L = 2-(ethylthio)-N-((pyridine-2-yl)methylene))benzenamine) is
synthesized and characterized by various spectroscopic techniques. The distorted octahedral
environment around osmium in the complex is confirmed by single crystal X-ray structure.
Cyclic voltammogram in acetonitrile exhibits Os(II)/Os(III) oxidation and ligand based
reduction. The complex effectively catalyzed the transfer hydrogenation reaction of ketones in
high yields in i-PrOH. The electronic structure and redox properties are interpreted by DFT
studies.
Keywords: Osmium carbonyl complex; X-ray structure; Electrochemistry; DFT calculation; Transfer
hydrogenation.
Corresponding author: Email: tkmondal@chemistry.jdvu.ac.in

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1. Introduction
The search for highly efficient transition metal homogeneous catalysts is a current issue of
industrial relevance for the synthesis of valuable organic compounds. In this context, ruthenium
and more recently osmium complexes are among the preferred metals because of their high
performance and versatility in a variety of processes [1]. Transfer hydrogenation is one of the
most important methods for the reduction of carbonyl compounds to their corresponding alcohols
[2-4] without the use of hazardous hydrogen gas or moisture-sensitive hydride reagents [5, 6].
Moreover, the transfer hydrogenation is widely accepted in industry as a cost-effective way for
the production of a number of hydroxylated organic products [7]. The catalytic hydrogenation of
carbonyl compounds are an elementary process for generated varieties of alcohols including
chiral compounds, which are ultimate worthy products and precursors for the agrochemical,
pharmaceutical, flavor, materials, and fine chemical industries [8-10].
The studies to develop the new catalysts for the transfer hydrogenation is still of
considerable interest for the finding of more efficient catalyst. The most efficient and selective
catalyst for transfer hydrogenation reactions are ruthenium, iridium and rhodium complexes [11-
15], while the osmium complexes are rarely used [16,17]. As a part of our ongoing research on
the synthesis, characterization and catalytic applications of transition metal complexes [18-22]
and to explore the chemistry of osmium carbonyls, herein we have synthesized a osmium(II)
carbonyl complex, [Os(H)(CO)(PPh3)2(L)]Cl (1) bearing triphenylphosphine with thioether
containing Schiff base ligand, 2-(ethylthio)-N-((pyridine-2-yl)methylene)benzenamine (L). An
array of tools including X-ray diffractometry, electrochemistry, and electronic absorption and
emission spectroscopy abetted with DFT calculations were used to characterize the complex.

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Further, the catalytic activity of the complex towards transfer hydrogenation of ketones was
investigated.
2. Experimental
2.1. Materials
2-(Ethylthio)-N-((pyridine-2-yl)methylene)benzenamine (L) was synthesized following the
reported procedure [23]. 2-Aminothiophenol, ethyl iodide, 2-formylpyridine and K2OsCl6.6H2O
were purchased from Sigma Aldrich. [Os(H)(Cl)(CO)(PPh3)3] was synthesized by reported
method [24]. All other chemicals and solvents were reagent grade and used as received.
2.2. Physical measurements
Microanalyses (C, H, N) data were obtained using a PerkinElmer Series-II CHN-2400 CHNS/O
elemental analyzer. Electronic spectra were measured on a Lambda 750 PerkinElmer
spectrophotometer in methanol. IR spectra were recorded on a RX-1 PerkinElmer spectrometer
in the range of 4000-400 cm-1 with the samples in the form of KBr pellets. Fluorescence spectra
were taken on a Shimadzu RF-6000 Spectrofluorophotometer. HRMS mass spectra were
obtained on a Waters (Xevo G2 Q-TOF) mass spectrometer. NMR spectra were recorded in
CDCl3 on a Bruker (AC) 300 MHz FT-NMR spectrometer in the presence of TMS as internal
standard. Cyclic voltammetric measurements were carried out using a CHI Electrochemical
workstation. A platinum wire working electrode, a platinum wire auxiliary electrode and
Ag/AgCl reference electrode were used in a standard three-electrode configuration. [Bu4N]PF6
was used as the supporting electrolyte in acetonitrile and the scan rate used was 50 mV s−1 under
nitrogen atmosphere.
Luminescence quantum yield was determined using carbazole as reference with a known
φR of 0.42 in MeCN. The complex and the reference dye were excited at the same wavelength,

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maintaining nearly equal absorbance (~0.1), and the emission spectra were recorded. The area of
the emission spectrum was integrated using the software available in the instrument and the
quantum yield is calculated according to the following equation:
2
2
φS/φR = [AS / AR ] x [(Abs)R /(Abs)S ] x [ηS /ηR ]
Here, φS and φR are the luminescence quantum yield of the sample and reference, respectively.
AS and AR are the area under the emission spectra of the sample and the reference respectively,
(Abs)S and (Abs)R are the respective optical densities of the sample and the reference solution at
the wavelength of excitation, and ηS and ηR are the values of refractive index for the respective
solvent used for the sample and reference.
Fluorescence lifetime was measured using a time-resolved spectrofluorometer from IBH,
UK. The instrument uses a picoseconds diode laser (NanoLed-03, 370 nm) as the excitation
source and works on the principle of time-correlated single photon counting [25]. The goodness
of fit was evaluated by χ2 criterion and visual inspection of the residuals of the fitted function to
the data.
2.3. Synthesis of [Os(H)(CO)(PPh3)2(L)]Cl (1)
To a suspension of [Os(H)(Cl)(CO)(PPh3)3] (0.223 g, 0.2 mmol) in dry toluene (20 mL), 2-
(ethylthio)-N-((pyridine-2-yl)methylene))benzenamine (L) (0.048 g, 0.2 mmol) was added and
the reaction mixture was refluxed for 10 h under N2 atmosphere to yield a dark brown solution.
The solvent was then removed under reduced pressure and the solid product of complex 1 was
washed with n-hexane several times to remove the PPh3. The product was air dried and collected.
Yield, 0.161 g (77%).
Anal. Calc. for C51H46ClN2OOsP2S (1): Calculated C, 55.90; H, 4.53; N, 2.74; S, 3.14. Found:
1
C, 55.6; H, 4.4; N, 2.6; S, 2.9. FT‒IR
υ
(KBr, cm-1): 2060 (Os-H), 1926(CO), 1582(C=N). H

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NMR (CDCl3, ppm): -9.85 ppm of Os-H peak (2JP-H, t, J = 20.3 Hz), 1.60 (3H, quartet , J = 7.6
Hz), 3.40 (2H, t, J = 8.2 Hz), 7.21 - 7.43 ppm (34H, m), 8.12 (1H, t, J=7.2 Hz), 8.41 (1H, d,
13
J=4.4 Hz), 8.51 (1H, d, J=4.8 Hz), 8.70 (1H, s). C {1H} NMR (CDCl3, ppm): 204.5 (C≡O),
31
155.2 (-HC=N), 117.2-141.6 (Ar C), 27.1 (-S-CH2-CH3), 15.2 (-S-CH2-CH3). P {1H} NMR
(CDCl3, ppm): 18.2 (s). UV-Vis in acetonitrile (λ (nm); ε, M-1cm-1): 471 (3424), 375 (6308), 315
(16433). ESI-MS m/z: 987.4106. E1/2 (OsII/OsIII): 1.15 V (∆E = 90 mV); Epc: -1.11 V.
2.4. Crystal structure determination and refinement
Single crystals of 1 were obtained by slow diffusion of n-hexane into dichloromethane solution
of the complex. X-ray data were collected using an automated Bruker AXS Kappa smart Apex-II
diffractometer equipped with an Apex-II CCD area detector using a fine focus sealed tube as the
radiation source of graphite monochromated Mo Kα radiation (λ = 0.71073 Å). Details of crystal
analyses, data collection and structure refinement are summarized in Table 1. Reflection data
were recorded using the ω scan technique. The structure was solved and refined by full-matrix
least-squares techniques on F2 using the SHELX-97 [26]. The absorption corrections were done
by multi-scan (SHELXTL program package) and all the data were corrected for Lorentz,
polarization effect. Hydrogen atoms were included in the refinement process as per the riding
model.
2.5. Computational method
Full geometry optimization was carried out by density functional theory (DFT) method using
B3LYP hybrid exchange correlation functional for the complex [27,28]. All elements except
osmium were assigned the 6-31G(d) basis set, whilst the LanL2DZ basis set with effective core
potential was employed for ruthenium atom [29-31]. Vibrational frequency calculations were
performed to ensure that the optimized geometries were local minima on the potential energy

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surface and only positive Eigen values were obtained. All calculations were performed with
Gaussian09 program package [32] with the aid of the GaussView, Version 5 visualization
program [33]. Vertical electronic excitations based on B3LYP optimized geometry were
computed using the time-dependent density functional theory (TDDFT) formalism [34-36] using
conductor-like polarizable continuum model (CPCM) [37-39] in acetonitrile to simulate the
solvent. GaussSum [40] was used to calculate the fractional contributions of various groups to
each molecular orbital.
2.6. Procedure for catalytic transfer hydrogenation
In a typical experiment the ketone (1 mmol), KOH (0.1 mmol), and osmium(II) complex (0.002
mmol) were added to 10 mL of 2-propanol, and the mixture was stirred at 80 °C in an inert
atmosphere. The reaction was then monitored at various time intervals by the use of GC. After
the reaction was complete, 2-propanol was removed on a rotary evaporator, and the resulting
semisolid was extracted with diethyl ether (5 × 10 mL). The extract was passed through a short
column of silica gel. The column was washed with ∼100 mL of diethyl ether. All the eluates
from the column were mixed, and the solvent from the mixture was evaporated off on a rotary
evaporator. The resulting residue was dissolved in 2-3 mL of hexane. Conversions were
determined by GC instrument equipped with a flame ionization detector (FID) using a HP-5
column of 30 m length, 0.53 mm diameter and 5.00 µm film thickness. The column, injector and
detector temperatures were 200, 250 and 250 ºC respectively. The carrier gas was N2 (UHP
grade) at a flow rate of 30 mL/min. The injection volume of sample was 2 µL. The alcohols were
identified by GC co-injection with authentic samples.
3. Results and discussion

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3.1. Synthesis and spectral characterization
The pseudo octahedral osmium(II) carbonyl complex, [Os(H)(CO)(PPh3)2(L)]Cl (1) (where L =
2-(ethylthio)-N-((pyridine-2-yl)methylene))benzenamine) was synthesized and characterized by
several spectroscopic techniques. The complex was synthesized by the reaction of
[Os(H)(Cl)(CO)(PPh3)3] and L in dry toluene under refluxing condition for 10 h (Scheme 1). IR
spectrum of the ligand shows a number of strong υ(C–H) bands at 2800–3100 cm-1. IR spectrum
of the complex exhibits sharp signal at 1926 cm-1 corresponds to υ(CO) along with a close by
weak peak at 2060 cm-1 corresponding to υ(Os-H). The υ(C=N) is significantly shifted to lower
frequency region compare to free ligand value suggesting the coordination of imine-N to osmium
[23]. 1H NMR spectrum of the complex was taken in CDCl3. All the expected signals including
1
aromatic protons are resolved. In the H NMR spectrum, S-CH2CH3 protons appeared at 1.60
ppm and 3.40 ppm. The triplet signal at -9.85 ppm (2JP-H, t, J=20 Hz) confirms the presence of
Os-H proton in the complex. A series of overlapping multiplet signals appeared in the region 7.2
to 8.7 ppm correspond to the protons of coordinated triphenylphosphine in the complex. The
UV-vis spectrum of the complex in acetonitrile exhibits a broad peak at 471 nm (ε, 3424 M-1cm-
1) along with two ligand centered peaks at 375 (ε, 6308 M-1cm-1) and 315 (ε, 16433 M-1cm-1) in
acetonitrile (Fig. 1).
S
S
PPh3
[Os(H)(Cl)(CO)(PPh3)3]
CO
N
Cl
N
Toluene / Reflux 10 h
Os
H
N
N
PPh3
L
[Os(H)(CO)(PPh3)2(L)]Cl (1)
Scheme 1. Synthesis of osmium carbonyl complex, [Os(H)(CO)(PPh3)2(L)]Cl (1)

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Upon excitation at 375 nm, an emission band at 477 nm with emission quantum yield (φ)
= 0.025 is observed for the complex in acetonitrile (Fig. 1). Lifetime data of the complex was
taken at 298 K in acetonitrile when excited at 370 nm. The emission decay curve was
deconvoluted with respect to the lamp profile. The observed florescence decay fits with bi-
exponential nature (Fig. 2). We have used mean fluorescence lifetime (τf = a1τ1 + a2τ2, where a1
and a2 are relative amplitude of decay process) to study the excited state stability of the complex.
The luminescence lifetime of the complex is found to be 2.63 ns.
3.2. Molecular Structure
The molecular structure of the complex was confirmed by single X-ray crystal structure study.
Selected bond distances and bond angles are summarized in Table 2. ORTEP plot with atomic
numbering is shown in Fig. 3. The molecule consists of a central osmium surrounded by six
donor centers, and the arrangement is distorted octahedral. The atomic arrangement involves two
trans-PPh3, chelating NN donors, hydrido (H-) and CO trans to the pyridyl-N donor within the
OsP2N2HC coordination sphere. The thioether containing NNS donor ligand coordinated through
imine-N and pyridyl-N atoms to the osmium centre, while –SR remain free and away from the
metal centre. The H- is located trans to the imine-N. The deviation of osmium coordination
sphere from ideal octahedron is because of the small bite angle of the five membered chelate ring
(Os1-N1-C6-C7-N8) [74.5(2)°]. The Os-N(imine) (Os1-N8, 2.168(6) Å) is significantly longer
than Os-N(pyridyl) (Os1-N1, 2.103(6) Å) distance. The trans phosphine angle P1-Os1-P2 of
168.23(6)° is found to be in the reported range [41].
3.3. DFT and TDDFT calculations
The geometry of complex 1 was optimized by DFT/B3LYP method to interpret the electronic
structure. Optimized bond distances and angles are well correlated with the X-ray crystal

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structure data (Table 2). The energy and compositions of selected molecular orbitals are
summarized in Table 3. Contour plots of selected molecular orbitals are given in Fig. 4. HOMO,
HOMO-2 and HOMO-3 of the complex are composed of dπ(Os) (49-55%) orbitals, the HOMO-
1 is 94% π(L) character. The LUMO and LUMO+1 have 91-94% π*(L) character, while
LUMO+2 to LUMO+5 have π(PPh3)character. The HOMO-LUMO energy gap is calculated to
be 3.07 eV.
To go deep insight into the electronic transitions in the complex vertical electronic
transitions were calculated using TDDFT/CPCM method in acetonitrile. The calculated vertical
electronic transitions are summarized in Table 4. The experimental band at 471 nm corresponds
to the admixture of HOMO → LUMO (λ = 485 nm, f = 0.0622) and HOMO-1 → LUMO (λ =
452 nm, f = 0.0904) transitions having mixed MLCT and ILCT character. The band at 375 and
315 nm corresponds to π(L) → π*(L) transitions having ILCT character.
3.4. Electrochemistry
The electrochemical behavior of the complex was investigated by cyclic voltammetry (CV) in
acetonitrile using tetrabutylammonium hexafluorophosphate [Bu4N]PF6 (0.1 M) as supporting
electrolyte and a Ag/AgCl reference electrode. When scanned in the potential range of -2.0 to 2.0
V, the complex exhibits one irreversible cathodic reduction peak at -1.11 V along with a quasi-
reversible oxidation couple with E1/2, 1.11 V (∆E = 90 mV) (Fig. 5). The irreversible cathodic
reduction peak corresponds to the ligand centered reduction as the LUMO of the complex has
91% π*(L) character. The oxidation process may be assigned as Os(II)/Os(III) oxidation couple
as HOMO has 55% dπ(Os) character.
3.5. Catalytic transfer hydrogenation reactions

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The transfer hydrogenation is an important and efficient reaction in organic synthesis. The
ruthenium(II) [41-43], rhodium [44-46] and iridium [47,48] complexes were used exclusively as
effective catalysts for transfer hydrogenation reactions. In comparison the catalytic properties of
osmium complexes is less explored [13]. That encourages us to synthesize new osmium-hydrido-
carbonyl complex and explore its catalytic properties towards transfer hydrogenation of ketones.
The results of the screening of the catalytic properties of complex 1 are described below.
In order to optimize the reaction conditions such as base, reaction time and
catalyst:substrate (C:S) ratios, the transfer hydrogenation of acetophenone to 1-phenylethanol in
presence of complex 1 as catalyst using i-PrOH as the solvent was carried out (Table 5). The
conversion rates were varied significantly with the base employed and a variety of base was
screened. The conversions were found to be very effective when KOH or NaOH was used as
base. The reaction rates were significantly decreased when weak base like Na2CO3 and
CH3COONa were used. A moderate conversion was observed in presence of KOtBu as base. The
progress of the conversion was also monitored with time to time and it was found that the
formation of 1-phenylethanol initially increased with the progress of the reaction and after 5 h no
appreciable change in conversion rate was observed. Again, to understand the catalytic efficiency
of the complex 1, different catalyst:substrate (C:S) ratios were tested. It is found that the
conversion is excellent in C:S ratio of 1:300 and with the variation of C:S ratio to 1:500, 1:700,
1:1000 or 1:1500, the reaction still proceeds but a sharp decrease in rate of conversion is
observed for C:S ratio 1:700 to 1:1500. The conversion (96%) is excellent with appreciable
turnover number (TON) when the C:S ratio is 1:500 and thus from this study it may be
concluded that this C:S ratio is the best choice for catalytic transfer hydrogenation reactions for
complex 1. A series of ketones were screened in transfer hydrogenation reaction using the

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optimum condition, C:S ratio of 1:500 and KOH as base. The results are summarized in Table 6.
The maximum conversion was observed for p-methoxycetophenone (98.2%). The conversions of
other acetophenones are found to be in the range 88-98%.
4. Conclusion
Herein, a new osmium(II) carbonyl complex, [Os(H)(CO)(PPh3)2(L)] (1) with thioether containg
NNS donor ligand (where L = 2-(ethylthio)-N-((pyridine-2-yl)methylene))benzenamine) is
synthesized and characterized by various spectroscopic techniques. X-ray structure confirms the
distorted octahedral environment around osmium. Cyclic voltammogram exhibits Os(II)/Os(III)
oxidation and ligand based reduction. The redox properties are well interpreted by theoretical
studies. Vertical electronic transitions calculated by TDDFT/CPCM method are used to interpret
the UV-Vis spectrum of the complex and a good correlation between experimental bands with
calculated transitions are observed. Moreover, the complex effectively catalyzed the transfer
hydrogenation reaction of ketones with high yields in i-PrOH.
Acknowledgment
Financial supports received from the Science and Engineering Research Board (SERB), New
Delhi, India (No. SB/EMEQ–242/2013 and YSS/2015/001533) is gratefully acknowledged. S.
Biswas and P. Roy are thankful to UGC, New Delhi, India for fellowship.
Supplementary materials
Crystallographic data for the structure 1 has been deposited with the Cambridge Crystallographic
Data center, CCDC No. 804954. Copies of this information may be obtained free of charge from
the Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (e-mail:
deposit@ccdc.cam.ac.uk or www:htpp://www.ccdc.cam.ac.uk).

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Table 1. Crystallographic data and refinement parameters for complex 1
Empirical formula
C52H47Cl3N2OSP2Os
Formula weight
Crystal system
Space group
1106.51
Triclinic
P
a / Å
b / Å
c / Å
13.7098(3)
14.3084(3)
15.1566(5)
104.4660(10)
107.1100(10)
107.5110(10)
2516.31(11)
2
α
β
γ
(º)
(º)
(º)
V / Å3
Z
calcd / g cm−3
1.460
ρ
/ mm−1
2.836
µ
T / K
293(2)
hklrange
F(000)
-17 to 17, -18 to 18, -19 to 19
1108
1.70 to 27.32
38855
θ
range (º)
Reflns collected
Unique reflns (Rint)
Observed data (I>2σ(I))
Data/restraints/parameters
R1a, wR2b (I>2σ(I))
R1, wR2 (all data)
GOFc
11338
10250
11338 / 0 / 542
0.0661, 0.1855
0.0714, 0.1914
1.071
Largest diff. peak/hole / e Å−3
1.632 / -0.959
a R1 = ∑ |(|Fo| – |Fc|)| / ∑ |Fo|
2
2 2
2
b wR2 = { ∑ [w (Fo –Fc2)2] / ∑ [w (Fo ) ] }1/2, w = 1/[σ2(Fo ) + (0.1305P)2 + 9.6342P], where P =
2
(Fo + 2Fc2)/3
2
2 2
c GOF = {∑ [w(Fo –Fc ) ] / (n–p)}1/2 , where n = number of measured data and p = number of
parameters.

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Table 2. Some Selected bond distances (Å) and angles (º) of complex 1
Bonds (Å)
Os1-H1
Os1-Cl7
Os1-N1
Os1-N8
Os1-P1
Os1-P2
O1-Cl7
X-ray
Calc.
1.626
1.871
2.178
2.256
2.461
2.433
1.167
1.63(2)
1.851(8)
2.103(6)
2.168(6)
2.3685(18)
2.3609(18)
1.152(10)
Angles (º)
N1-Os1-H1
N1-Os1- C17
N1-Os1-N8
N1-Os1-P1
N1-Os1-P2
N8-Os1-H1
N8-Os1- C17
N8-Os1-P1
N8-Os1-P2
C17-Os1-H1
C17-Os1-P1
C17-Os1-P2
P1-Os1-H1
P1-Os1-P2
P2-Os1-H1
88.7(7)
90.534
178.376
74.522
90.884
91.589
164.913
103.870
98.575
96.462
91.062
89.583
88.359
83.443
164.877
81.618
179.2(3)
74.5(2)
91.17(17)
91.22(17)
162.4(7)
106.3(3)
99.26(17)
92.48(17)
90.6(7)
88.8(2)
88.7(2)
85.8(7)
168.23(6)
82.8(7)

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Table 3. Energy and compositions of some selected molecular orbitals of 1
MO
Energy (eV)
% of composition
Os
05
08
07
13
02
05
55
03
54
49
06
14
03
11
10
04
03
L
CO
02
01
01
01
02
01
0
PPh3
92
79
89
83
03
03
30
03
10
41
21
82
96
82
38
86
42
LUMO+5
LUMO+4
LUMO+3
LUMO+2
LUMO+1
LUMO
-2.82
-2.91
-2.93
-3.21
-3.71
-4.95
-8.02
-8.14
-8.56
-8.71
-8.77
-8.83
-8.90
-8.89
-9.02
-9.05
-9.08
02
13
04
03
94
91
15
94
22
04
72
02
01
05
50
09
55
HOMO
HOMO-1
HOMO-2
HOMO-3
HOMO-4
HOMO-5
HOMO-6
HOMO-7
HOMO-8
HOMO-9
HOMO-10
01
13
06
01
02
0
02
02
01
0

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Table 4. Vertical electronic excitations calculated by TDDFT/CPCM method of complex 1
Eexcitation λexcitation Osc.
Key transitions
Charactera
(eV)
(nm)
strength (f)
0.0622
(94%)HOMO → LUMO
(87%)HOMO-1 → LUMO
(90%)HOMO-2 → LUMO+1
dπ(Os) → π*(L), MLCT
π(L) → π*(L), ILCT
dπ(Os)/ π(L) → π*(L),
MLCT/ ILCT
2.5541 485.44
2.7414 452.27
3.1371 395.22
0.0904
0.0193
π(L) → π*(L), ILCT
π(L) → π*(L), ILCT
π(L) → π*(L), ILCT
3.5543 348.83
3.9821 311.36
0.1449
0.0989
0.0514
(76%)HOMO-4 → LUMO
(82%)HOMO-8 → LUMO
(63%)HOMO-10 → LUMO
4.1779 296.76
a
MLCT: metal to ligand charge transfer transition and ILCT: intra-ligand charge transfer
transition

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Table 5. Effect of S:C ratio, base and reaction time on the transfer hydrogenation of
acetophenonea
O
OH
Complex 1
i-PrOH, Base
Entry
1
S:C ratio
Base
Time (h)
Conversionb (%)
TONc
216
255
291
291
291
288
114
96
1:300
1:300
1:300
1:300
1:300
1:300
1:300
1:300
1:300
1:500
1:700
1:1000
1:1500
KOH
KOH
KOH
KOH
KOH
NaOH
Na2CO3
3
4
5
7
10
5
5
5
5
5
5
5
5
72
85
97
97
97
96
38
32
63
96
83
42
25
2
3
4
5
6
7
8
CH3COONa
9
KOtBu
KOH
KOH
KOH
KOH
189
480
581
420
375
10
11
12
13
a
Reaction condition: acetophenone (3 mmol), complex 1 (10-2
µmol), catalyst:KOH 1:4 in i-
b
c
PrOH (10 mL) at 80 ºC; Conversion was determined by GC analysis; Turnover number
(TON) = mole of product/mol of catalyst.

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Table 6. Transfer hydrogenation of ketones using complex 1a
Entry Ketones
1
Alcohols
Conversion TONc
(%)b
Entry
7
Ketones
Alcohols
Conversion TONc
(%)b
96
480
92
460
OH
2
3
95
95
475
475
8
9
93
96
465
480
4
5
93
95
98
465
475
490
10
11
12
94
93
89
470
465
445
O
O
6
O
a Experimental condition: reactions were carried out at 80 °C, ketone (3 mmol), Os (II) complex (0.2 mol%), KOH (0.1 mmol), i-PrOH (10 mL); b
Conversion was determined by GC analysis; c Turnover number (TON) = mole of product/mol of catalyst

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Figure captions
Fig. 1. UV-vis (─) and emission (─) spectra of 1 in acetonitrile.
Fig. 2. Life time decay profile of 1 in acetonitrile (λexcitation = 370 nm).
Fig. 3. ORTEP plot with 35% ellipsoidal probability of 1.
Fig. 4. Contour plots of some selected molecular orbitals of 1. Isodensity value 0.04 e Bohr-3.
Fig. 5. Cyclic voltammogram of complex 1 in acetonitrile.

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Fig. 1

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1000
100
10
1
0
10
20
30
40
50
60
τ
(ns)
Fig. 2

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Fig. 3

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HOMO
HOMO-1
HOMO-2
LUMO
LUMO+1
LUMO+2
Fig. 4

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Fig. 5

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HIGHLIGHTS
•
•
•
•
•
A new osmium(II) carbonyl complex with thioether containg NNS donor ligand is
synthesized and characterized.
Single crystal X-ray structure exhibits distorted octahedral environment around osmium
in the complex.
Cyclic voltammogram in acetonitrile exhibits Os(II)/Os(III) oxidation and ligand based
reduction in the complex.
The complex effectively catalyzed the transfer hydrogenation reaction of ketones with
high yields in i-PrOH.
The electronic structure and redox properties of the complex are interpreted by DFT
studies.