Synthesis of thiolato bridged dimeric rhodium(III) triphenylphosphine complex via C–S bond cleavage: X-ray structure, DFT computation and catalytic evaluation towards transfer hydrogenation of ketones

Article abstract of DOI:10.1016/j.molstruc.2019.126932

Herein, we have synthesized a new dimeric rhodium(III) triphenylphospine complex, [Rh₂(PPh₃)₂(L)₂Cl₂] (1) via sp³(C)–S bond cleavage of a thioether containing ligand, 1-(((2-(ethylthio)phenyl)diazenyl)methyl)naphthalen-2-ol (L-CH₂CH₃). The complex was thoroughly characterized by using various spectroscopic techniques. Dimeric structure with distorted octahedral geometry of each of the rhodium center is confirmed by single crystal X-ray diffraction method. Catalytic efficiency of the complex towards transfer hydrogenation of ketones is studied in i-PrOH. Electronic structure and UV–vis spectrum of the complex are interpreted by DFT and TDDFT computations.

Full text of DOI:10.1016/j.molstruc.2019.126932

Journal of Molecular Structure 1198 (2019) 126932
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Synthesis of thiolato bridged dimeric rhodium(III) triphenylphosphine
complex via CeS bond cleavage: X-ray structure, DFT computation and
catalytic evaluation towards transfer hydrogenation of ketones
,
, *
Puspendu Roy a b, Rahul Naskar a, Chandan Kumar Manna a, Tapan Kumar Mondal a
a Department of Chemistry, Jadavpur University, Kolkata, 700032, India
b Department of Chemistry, Netaji Nagar Day College, University of Calcutta, Kolkata, 700092, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Herein, we have synthesized a new dimeric rhodium(III) triphenylphospine complex, [Rh2(PPh3)2(L)2Cl2]
(1) via sp3(C)eS bond cleavage of a thioether containing ligand, 1-(((2-(ethylthio)phenyl)diazenyl)
methyl)naphthalen-2-ol (L-CH2CH3). The complex was thoroughly characterized by using various spec-
troscopic techniques. Dimeric structure with distorted octahedral geometry of each of the rhodium
center is confirmed by single crystal X-ray diffraction method. Catalytic efficiency of the complex to-
wards transfer hydrogenation of ketones is studied in i-PrOH. Electronic structure and UVevis spectrum
of the complex are interpreted by DFT and TDDFT computations.
Received 16 April 2019
Received in revised form
31 July 2019
Accepted 14 August 2019
Available online xxx
Keywords:
Dimeric rhodium(III) complex
CeS bond cleavage
© 2019 Elsevier B.V. All rights reserved.
Transfer hydrogenation of ketones
DFT calculation
1. Introduction
alcohols has received considerable attention in chemical research
because of its capacity to hydrogenate substrates in mild conditions
Transition metal mediated CeS bond activation, cleavage and
transformation reactions are extensively studied for the last few
decades owing to their importance in petroleum industry [1e3],
synthetic chemistry [4e6], biorganic and bioinorganic chemistry
[7e10]. The ligand systems played a crucial role in the metal
catalyzed CeS bond activation. For desired reactivity, the binding
affinity and the size of the ligands, electron density and steric fac-
tors of the ligands are tuned in the complexes [11,12]. More and
more attentions are given to this research topic to explore conve-
nient and efficient strategy. Recently, Majumdar et al. are exten-
sively studied the iron and cobalt mediated CeS bond activation
reactions and explored their chemical reactivity [13e15]. Hosoya
et al. are reported the metal catalyzed selective aromatic CeS bond
cleavage triggered transformations of thioarenes [16]. Shi et al. have
successfully utilized rhodium catalyzed CeS bond activation to
construct CeC bond [17]. Liebeskind and co-workers have reported
the palladium and copper catalyzed cross coupling reactions via
CeS bond cleavage reactions [18e20].
[21e23] and avoids the use of high pressure vessels and com-
pressed H2 or moisture-sensitive hydride reagents [24e27]. People
are deeply engaged to develop new catalysts for future industrial
applications in terms of selectivity, efficiency, scope, simplicity and
economic viability [28e31]. In our continued efforts to design and
synthesis of platinum group metal complexes and to explore their
catalytic activity towards transfer hydrogenation of ketones
[32e35] herein, we have synthesized a new dimeric rhodium(III)
triphenylphospine complex, [Rh2(PPh3)2(L)2Cl2] (1) via CeS bond
cleavage of a thioether containing ligand, 1-(((2-(ethylthio)phenyl)
diazenyl)methyl)naphthalen-2-ol (L-CH2CH3). The coordination
chemistry of Pd(II) and Pt(II) with L-CH2CH3 was explored previ-
ously [36,37]. Recently, rhodium and iridium assisted sp2(C)eS
bond cleavage and formation of cyclometalated complexes were
reported by S. Acharya et al. [38]. In the present work we have
synthesized the dimeric Rh(III) complex by sp3(C)eS bond cleavage
of L-CH2CH3. Moreover, the catalytic efficiency of the complex to-
wards transfer hydrogenation of ketones is studied in i-PrOH.
Structure of the complex is confirmed by single crystal X-ray
diffraction method. Electronic structure of the complex is inter-
preted by DFT computations.
The transfer hydrogenation of ketones to the corresponding
* Corresponding author.
E-mail address: tapank.mondal@jadavpuruniversity.in (T.K. Mondal).
https://doi.org/10.1016/j.molstruc.2019.126932
0022-2860/© 2019 Elsevier B.V. All rights reserved.

2
P. Roy et al. / Journal of Molecular Structure 1198 (2019) 126932
Table 1
2. Experimental
Crystallographic data and refinement parameters of [Rh2(PPh3)2(L)2Cl2] (1).
2.1. Material and methods
Formula
C70H54Cl6N4O2P2Rh2S2
Formula Weight
Crystal System
Space group
a, b, c [Å]
1527.75
Monoclinic
C2/c
23.9738(14),9.6124(5),30.0374(16)
90
109.396(4)
90
6529.1(6)
4
1.554
0.914
3088
multi-scan
296(2)
0.71073
Ligand, L-CH2CH3 was synthesized following the reported
method [36]. 2-Aminothiophenol and [Rh(PPh3)3Cl] were pur-
chased from Sigma Aldrich. Other chemicals and solvents were
reagent grade and used as received. For spectroscopic studies HPLC
grade solvents were used. Microanalyses (C, H, N) data were ob-
tained using a PerkinElmer Series-II CHN-2400 CHNS/O elemental
analyzer. Electronic spectra were measured on a Lambda 750 Per-
kinElmer spectrophotometer in the range 250e900 nm in aceto-
a
b
g
V [ Å3]
Z
D(calc) [g/cm3]
Mu(MoKa) [/mm]
F(000)
nitrile. IR spectra were recorded as KBr pellets on
a RX-1
PerkinElmer spectrometer in the range of 400e4000 cmꢀ1. 1H NMR
spectrum was taken on a Bruker (AC) 300 MHz FT-NMR spec-
trometer in CDCl3.
Absorption Correction
Temperature (K)
Radiation [Å]
q
(Min-Max) [ꢂ]
1.44e25.00
Dataset (h; k; l)
Reflns collected/Unique reflns/R(int)
Observed data (I > 2s(I))
ꢀ28 and 28; ꢀ11 and 11; ꢀ36 and 35
2.2. Synthesis of [Rh2(PPh3)2(L)2Cl2] (1)
36061/5619/0.1158
2762
Data/restraints/parameters
5619/0/397
0.0819, 0.1398
1.061
1.460/ꢀ0.854
Rh(PPh3)3Cl (0.380 g, 0.4 mmol) was dissolved in 20 mL of
acetonitrile. To it 10 mL acetonitrile solution of L-CH2CH3 (0.124 g,
0.4 mmol) was added and the reaction mixture was refluxed for 8 h
under N2 atmosphere. The reaction mixture was cooled and the
solvent was removed under reduced pressure. The crude product
was purified by column chromatography using a silica gel (mesh
60e120). A pink coloured band of the complex (1) was eluted by
50% (v/v) ethyl acetate-petroleum ether solvent mixture. The sol-
vent was removed under reduced pressure the pure complex 1 was
obtained as a pink solid which was further dried under vacuum.
Yield was, 0.205 g, 70%.
R1a, wR2b (I > 2
s(I))
GOFc
Largest diff. peak/hole/e Åꢀ3
P
P
a
R1
¼
|(|Fo| e |Fc|)|/ |Fo|.
P
P
b
wR2 ¼ { [w (F2oeFc2)2]/ [w (Fo2)2] }1/2, w ¼ 1/[
s
2(F2o) þ (0.0357P)2 þ 25.2136P],
where P ¼ (F2o þ 2Fc2)/3.
P
c
GOF ¼ {
[w(Fo2eFc2)2]/(nep)}1/2
,
where n ¼ number of measured data and
p ¼ number of parameters.
dependent density functional theory (TDDFT) formalism [44e47]
and the solvent effect (acetonitrile) was simulated using the
conductor-like polarizable continuum model (CPCM) [48e50]. All
computations were carried out using the Gaussian09 (G09) pro-
gram [51]. GaussSum [52] program was used to calculate the frac-
tional contributions of various groups to each molecular orbital for
1.
Anal. Calc. for C68H50Cl2N4O2P2Rh2S2 (1): C, 60.14; H, 3.71; N,
4.13; Found: C, 59.92; H, 3.65; N, 4.03; IR data (KBr, cmꢀ1): 747, 688,
512 (coordinated PPh3), 1404 y
(N]N). 1H NMR data (CDCl3, ppm):
7.24 (PPh3), 7.04e8.23 (other aromatic protons). UVeVis (in
acetonitrile), lmax (nm) (ε ꢁ 10ꢀ3
,
molꢀ1cmꢀ1): 320(19.55),
371(16.49), 422(sh), 515(7.43), 595(12.54).
2.5. General procedure for the transfer hydrogenation of ketones
2.3. Crystallography
In a typical transfer hydrogenation reaction a solution complex 1
(0.004 mmol), KOH (0.02 mmol) and the corresponding ketone
(2 mmol) was dissolved in 10 mL i-PrOH. The reaction mixture was
degassed and refluxed at 80 ꢂC under stirring condition. The reac-
tion was monitored at various time intervals by GC using authentic
sample. After the completion of the reaction, i-PrOH was removed
under reduced pressure and extracted with diethyl ether. The
conversion was determined by GC equipped with a flame ionization
detector (FID) and HP-5 column of 30 m length, 0.53 mm diameter
Single crystals of [Rh2(PPh3)2(L)2Cl2] (1) were grown by slow
diffusion of n-hexane into dichloromethane solution of the com-
plex. Single crystal data were collected using the
with an automated Bruker SMART APEX CCD diffractometer using
graphite monochromated MoK radiation (
u scan technique
a
l
¼ 0.71073 Å) at room
temperature. Selected data collection parameters and other crys-
tallographic results are summarized in Table 1. Reflection data were
recorded using the
u scan technique. The structure was solved by
direct methods and refined by full-matrix least-squares on F2
techniques with anisotropic displacement parameters for all non-
hydrogen atoms using SHELXL-97 [39]. The absorption correc-
tions 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.
and 5.00 mm film thickness. The column, injector and detector
temperatures were 200, 250 and 250 ꢂC respectively. The carrier
gas was N2 (UHP grade) at a flow rate of 30 mL/min. The injection
volume of sample was 2 mL. The alcohols were identified by GC
using undecane as an internal standard and each of the catalytic
run was performed three times.
2.4. Computational method
3. Results and discussion
Gas phase geometry of [Rh2(PPh3)2(L)2Cl2] (1) was fully opti-
mized without any symmetry constraints in singlet ground-state by
DFT/B3LYP [40,41] method. For rhodium atom LanL2DZ basis set
with effective core potential was employed [42e44]. For all ele-
ments 6-31 þ G(d) basis set was used. The vibrational frequency
calculation was performed to ensure that the optimized geometry
represents real minimum of the ground state potential energy
surface. Electronic spectrum was computed using the time-
3.1. Synthesis and spectral characterization
The dimeric rhodium(III) triphenylphosphine complex,
[Rh2(PPh3)2(L)2Cl2] (1) was synthesized by the reaction of
Rh(PPh3)3Cl and azo-thioether ligand, L- SCH2CH3 under refluxing
condition in acetonitrile (Scheme 1). The complex was thoroughly
characterized by several spectroscopic techniques. IR spectrum of
the complex exhibits y
(N]N) peak at 1404 cmꢀ1 which is lower

P. Roy et al. / Journal of Molecular Structure 1198 (2019) 126932
3
Table 2
Selected X-ray and calculated bond distances and angles of 1.
N
N
S
Cl
Bonds(Å)
X-ray
Calc.
Cl
S
S
O
Rh(PPh3)3Cl
Rh
Rh1eN1
Rh1eO1
Rh1eS1
Rh1eP1
Rh1eCl1
Rh1eS1i
S1eC1
1.956(7)
2.026(6)
2.253(3)
2.318(2)
2.346(2)
2.686(4)
1.761(10)
1.272(10)
1.279(8)
2.047
2.069
2.363
2.408
2.404
2.492
1.782
1.286
1.276
N
N
OH
Rh
O
Reflux in CH3CN for 8 h
N
N
Ph3P
Ph3P
[Rh2(PPh3)2(L)2Cl2] (1)
L-CH2CH3
O1eC8
N1eN2
Scheme 1. Synthesis of dimeric rhodium(III) complex, [Rh2(PPh3)2(L)2Cl2] (1).
Angles (ꢂ)
than the free ligand value [36]. 1H NMR spectrum of the complex
was taken in CDCl3. All the expected proton signals of the ligands
including aromatic protons are resolved except SeCH2CH3 peaks,
which suggests the CeS bond cleavage in the complex. A series of
overlapping multiplet signals appeared in the region
7.24e8.23 ppm correspond to the protons of coordinated triphe-
nylphosphine along with azo-thiophenolato ligand in the complex.
The UVevis spectrum of the complex in acetonitrile exhibits a low
energy sharp peak at 595 nm (ε ꢁ 10ꢀ3, 12.54 Mꢀ1cmꢀ1) along with
a shoulder peak at 515 nm (ε ꢁ 10ꢀ3, 7.43 Mꢀ1cmꢀ1). In addition,
N1eRh1eO1
N1eRh1eS1
N1eRh1eS1i
N1eRh1eCl1
N1eRh1eP1
O1eRh1eS1
O1eRh1eS1i
O1eRh1eCl1
O1eRh1eP1
S1eRh1eS1i
S1eRh1eP1
S1eRh1eCl1
Rh1eS1eRh1
91.4(3)
87.4(2)
89.796
85.609
95.897
177.898
93.911
171.157
90.555
88.252
91.431
82.421
96.410
96.221
97.559
87.59(19)
175.8(2)
91.32(19)
173.5(2)
93.7(2)
87.02(17)
91.2(2)
79.95(15)
95.19(12)
93.73(10)
99.88(15)
two ligand centered peaks appeared at 371 nm (ε ꢁ 10ꢀ3
,
16.49 Mꢀ1cmꢀ1) and 320 nm (ε ꢁ 10ꢀ3, 19.55 Mꢀ1cmꢀ1) in aceto-
nitrile (Fig. 1).
3.2. Molecular structure
Single crystals of [Rh2(PPh3)2(L)2Cl2] (1) suitable for structure
determination were grown by slow diffusion of n-hexane into
dichloromethane solution of the complex. The molecular structure
of 1 was unambiguously confirmed by single crystal X-ray structure
analysis. The molecule is crystallized in monoclinic crystal system
with C2/c symmetry. Detailed crystallographic information and
data collection are summarized in Table 1. Selected bond lengths
and bond angles of the complex are given in Table 2. The ORTEP plot
of the dimeric complex is represented in Fig. 2. Each of the rhodium
center of the dimeric complex has pseudo octahedral environment.
The thiophenolato ligand L coordinated to Rh center through azo-N,
phenolic-O and thiophenolato-S atoms. The thiophenolato-S
bridges between the two rhodium centers in the dimeric complex
30
25
20
15
10
5
Fig. 2. ORTEP plot with 35% ellipsoidal probability of [Rh2(PPh3)2(L)2Cl2] (1) (solvent,
CH2Cl2 is omitted for clarity).
0
300
400
500
600
700
(nm)
with RheS distances of 2.253(3) and 2.686(4) Å. RheN(azo) dis-
tance is found to be 1.956(7) Å (Rh1eN1) in the complex. The RheP
Fig. 1. UVevis spectrum of 1 in acetonitrile.

4
P. Roy et al. / Journal of Molecular Structure 1198 (2019) 126932
Table 3
ray crystal structure data (Table 2). HOMO and HOMO-1of the
complex has 86% ligand character along with reduced contribution
Energy and compositions of some selected molecular orbitals of 1.
of d
acter. HOMO-3 to HOMO-7 has mixed d
(23e47%) and
(L) (23e56%) character. LUMO and LUMOþ1 of the
complex has 87e90%
has mixed contribution of dp(Rh) (31e52%) and p*(L) (30e40%)
orbitals (Table 3, Fig. 3).
p
(Rh) (5e10%). HOMO-2 has 72% p
p
(Cl) and 15% d
p
(Rh) char-
MO
Energy
% of composition
p
(Rh) (13e28%), p
p(Cl)
Rh
L
PPh3
Cl
p
LUMOþ5
LUMOþ4
LUMOþ3
LUMOþ2
LUMOþ1
LUMO
ꢀ1.06
ꢀ1.12
ꢀ1.66
ꢀ1.81
ꢀ2.30
ꢀ2.38
ꢀ5.07
ꢀ5.23
ꢀ5.42
ꢀ5.70
ꢀ5.73
ꢀ5.74
ꢀ6.07
ꢀ6.10
ꢀ6.24
ꢀ6.28
ꢀ6.39
51
52
31
37
08
06
05
10
15
21
13
28
18
15
02
04
10
38
30
40
38
87
90
86
86
08
35
35
23
56
34
78
77
55
01
04
28
23
05
03
09
01
05
10
16
02
04
12
07
18
14
10
13
01
3
0
0
p
*(L) character, while LUMOþ2 to LUMOþ5
To get deep insight into the electronic transition of the complex
vertical electronic transitions were calculated by TDDFT method
using CPCM model in acetonitrile. Calculated vertical electronic
transitions of 1 are summarized in Table 4. The experimental low
energy band at 595 nm corresponds to the HOMO / LUMO tran-
sition (lcalc. ¼ 574 nm) having ILCT (intra-ligand charge transfer
transition) character. The band at 515 nm of the complex again has
ILCT character corresponds to HOMO-1/LUMOþ1 transition
HOMO
0
HOMO-1
HOMO-2
HOMO-3
HOMO-4
HOMO-5
HOMO-6
HOMO-7
HOMO-8
HOMO-9
HOMO-10
03
72
34
36
47
23
39
13
01
21
(
lcalc. ¼ 525 nm). The shoulder peak at 422 nm has mixed MLCT
(metal to ligand charge transfer transition) and ILCT character,
while the high energy peaks at 371 and 320 nm correspond to ILCT
transitions in the complex.
(Rh1eP1, 2.318(2) Å) and RheCl (Rh1eCl1, 2.346(2) Å) bond dis-
tances are found as expected for other rhodium triphenylphos-
phine complexes [53,54]. The rhodium coordination sphere
deviates from ideal octahedron and significant deviation of bond
angle is detected for S1eRh1eS1i, 79.95(15)ꢂ.
3.4. Catalytic transfer hydrogenation reactions
The synthesized Rh(III) complex was employed as catalyst for
transfer hydrogenation of ketones which is a significant and useful
process in organic synthesis. The catalytic reaction conditions were
optimized with respect to bases, catalyst loading and reaction time.
The transfer hydrogenation of acetophenone to 1-phenylethanol
was chosen as a standard reaction in i-PrOH. The results of trans-
fer hydrogenation of acetophenone (2 mmol) using 0.5 mol% of
complex 1 and 0.02 mmol of different bases are summarized in
Table 5. In case of weak bases such as Na2CO3 and CH3COONa the
3.3. DFT and TDDFT calculations
Geometry optimization of 1 was carried out by using DFT/B3LYP
method to interpret the electronic structure of the complex. The
optimized bond distances and angles are well reproducing the X-
HOMO
HOMO-1
HOMO-2
LUMO
LUMO+1
LUMO+2
Fig. 3. Contour plots of selected molecular orbitals of [Rh2(PPh3)2(L)2Cl2] (1). Isodensity value 0.04 e Bohrꢀ3
.

P. Roy et al. / Journal of Molecular Structure 1198 (2019) 126932
5
Table 4
Vertical electronic transition calculated by TDDFT/CPCM method of 1.
l
(nm)
E (eV)
Osc. Strength (f)
0.2462
Key excitations
Character
lexpt. (nm) (10ꢀ3ε, Mꢀ1cmꢀ1
)
574.1
525.2
2.1598
(95%)HOMO/LUMO
p
ILCT
p
(L)/
p
(L*)
(L*)
595(12.54)
2.3608
0.1319
(73%)HOMO-1/LUMOþ1
(L)/p
515(7.43)
ILCT
432.5
426.2
405.7
372.7
2.8667
2.9091
3.0562
3.3267
0.0634
0.1677
0.1869
0.1562
(76%)HOMO-3/LUMO
(67%)HOMO-2/LUMOþ1
(65%)HOMO-6/LUMOþ1
(63%)HOMO-8/LUMO
d
d
d
p
ILCT
p
p
p
(Rh)/
(Rh)/
(Rh)/
p
p
p
(L)/
(L)/
(L)/
p(L*) MLCT/ILCT
p(L*) MLCT/ILCT
p(L*) MLCT/ILCT
422(sh)
(L)/
p
(L*)
371(16.49)
320(19.55)
327.5
3.7860
0.2560
(61%)HOMO-9/LUMOþ1
p
ILCT
(L)/p
(L*)
Table 5
Effect of bases and reaction time on the transfer hydrogenation of acetophenonea.
O
OH
1
Complex
i-PrOH, Base
Entry
Base
Time (h)
Conversionb (%)
1
2
3
4
5
6
7
8
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
2
3
4
5
6
7
8
9
10
5
5
5
5
57.1
76.2
89.5
97.9
98.0
98.1
98.3
98.4
98.6
96.3
43.8
37.2
71.5
9
KOH
10
11
12
13
NaOH
Na2CO3
CH3COONa
KOtBu
a
Reaction condition: acetophenone (2 mmol), complex 1 (0.5 mol %), catalyst:base 1:4 in i-PrOH (10 mL) at 80 ꢂC.
Conversion was determined by GC with undecane as an internal standard.
b
conversions were significantly low (37e44%), whereas a moderate
conversion was observed in case of KOtBu (72%). The catalytic
conversions were significantly enhanced with strong bases such as
KOH or NaOH (96e98%). Hence KOH was chosen as base in all re-
actions. Furthermore, the catalytic conversions with different time
intervals were also monitored and the maximum conversion was
achieved within the 5 h of reaction (Fig. 4). To explore the efficiency
of the catalyst towards transfer hydrogenation reaction, low cata-
lyst loading test was carried out. The reactions were screened using
1.0e0.05 mol% of catalyst concentration. For 0.05 and 0.1 mol% of
the catalyst loading the conversion rates were significantly drop-
ped with high turnover numbers (TONs), while maximum con-
versions were achieved in minimum 0.2 mol% of the catalyst with
appreciable turnover number (TON) (Table 6). So, 0.2 mol% catalyst
concentration was used for all catalytic reactions.
A series of ketones were screened in transfer hydrogenation
reactions using C:S ratio of 1:500 and KOH as base in i-PrOH. The
results transfer hydrogenation of ketones are summarized in
Table 7. The maximum conversion was observed for p-methox-
ycetophenone (98%) to corresponding alcohol. The conversions of
other acetophenones were found to be in the range 91e97%.
Excellent catalytic conversions were also achieved for cyclic ke-
tones such as cyclopentanone (97%), cyclohexanone (94%) and
100
90
80
70
60
50
2
4
6
8
10
Time (h)
Fig. 4. Time dependence of the catalytic transfer hydrogenation of acetophenone using
1 mol % catalyst 1 in i-PrOH at 82 ꢂC with KOH as base.

6
P. Roy et al. / Journal of Molecular Structure 1198 (2019) 126932
Table 6
4. Conclusion
Effect of low catalyst loadinga.
Entry
Mol % of 1
Conversionb (%)
TONc
A
new dimeric rhodium(III) triphenylphospine complex,
[Rh2(PPh3)2(L)2Cl2] (1) is synthesized by sp3(C)eS bond cleavage of
a thioether containing ligand, 1-(((2-(ethylthio)phenyl)diazenyl)
methyl)naphthalen-2-ol (L-CH2CH3). The complex is thoroughly
characterized by several spectroscopic techniques. Structure of the
complex is confirmed by single crystal X-ray diffraction method.
The complex exhibits excellent catalytic activity towards transfer
hydrogenation of ketones in i-PrOH using KOH as base. Electronic
structure and solution spectrum of the complex are well inter-
preted by DFT and TDDFT computations.
1
2
3
4
5
6
7
8
9
1.0
0.75
0.5
0.3
0.25
0.2
0.15
0.1
0.05
98.9
98.3
97.9
97.5
97.3
97.2
83.6
72.3
47.5
99
131
196
325
389
486
557
723
950
a
Reaction condition: acetophenone (2 mmol), complex 1 (0.05e1.0 mol%), cata-
lyst:base 1:4 in i-PrOH (10 mL) at 80 ꢂC for 5 h.
b
Conversion was determined by GC with undecane as an internal standard.
Turnover number (TON) ¼ mole of product/mol of catalyst.
c
Supplementary materials
Crystallographic data for the structure of 1 has been deposited
with the Cambridge Crystallographic Data center, CCDC No.
1891313. 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).
cycloheptanone (92%). Moreover, the catalytic efficiency of the
present rhodium(III) complex towards transfer hydrogenation of
ketones are comparable to the reported rhodium catalysts
[35,55e57].
Table 7
Transfer hydrogenation of ketones using complex 1a.
1
Complex
O
OH
OH
O
C : S = 1: 500
+
+
R1
R2
R1
R2
KOH, Reflux for 5 h
Entry
1
Ketones
Alcohols
Conversion (%)b
TONc
486
Entry
6
Ketones
Alcohols
Conversion (%)b
90.5
TONc
453
97.2
O
OH
O
OH
2
3
94.1
95.7
471
479
7
8
92.3
97.1
462
486
O
O
OH
OH
OH
O
O
O
OH
OH
Cl
Cl
Br
4
5
a
95.2
97.9
476
490
9
94.3
91.7
472
459
O
OH
Br
10
O
OH
O
OH
O
O
Experimental condition: reactions were carried out at 80 ꢂC, ketone (2 mmol), Rh(III) complex (0.2 mol%), KOH (0.02 mmol), i-PrOH (10 mL).
Conversions were determined by GC with undecane as an internal standard and were reported mean values of three runs.
Turnover number (TON) ¼ mole of product/mol of catalyst.
b
c

P. Roy et al. / Journal of Molecular Structure 1198 (2019) 126932
7
[31] O. Altan, M.K. Yilmaz, J. Organomet. Chem. 861 (2018) 252e262.
[32] S. Biswas, D. Sarkar, P. Roy, T.K. Mondal, Polyhedron 131 (2017) 1e7.
Acknowledgment
[33] S. Biswas, D. Sarkar, S. Kundu, P. Roy, T.K. Mondal, J. Mol. Struct. 1099 (2015)
297e303.
[34] S. Biswas, P. Roy, S. Jana, T.K. Mondal, J. Organomet. Chem. 846 (2017)
201e207.
[35] P. Roy, C.K. Manna, R. Naskar, T.K. Mondal, Polyhedron 158 (2019) 208e214.
[36] S. Acharya, A. Kejriwal, A.N. Biswas, P. Das, D.N. Neogi, P. Bandyopadhyay,
Polyhedron 38 (2018) 50e57.
[37] S. Acharya, A. Kejriwal, A.N. Biswas, P. Das, D.N. Neogi, P. Bandyopadhyay,
Inorg. Chim. Acta 394 (2013) 757e764.
Financial supports received from the Science and Engineering
Research Board (SERB), New Delhi, India (File No. EEQ/2018/
000266) is gratefully acknowledged. TKM is also grateful to JU-
RUSA 2.0 program for research support. P. Roy and R. Naskar are
thankful to UGC, New Delhi, India for fellowship.
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