Synthesis of new rhodium(III) complex by benzylic C[sbnd]S bond cleavage of thioether containing NNS donor Schiff base ligand: Investigation of catalytic activity towards transfer hydrogenation of ketones

Article abstract of DOI:10.1016/j.ica.2020.120096

A new rhodium(III)-triphenylphosphine mixed ligand complex, [Rh(PPh₃)(L)Cl₂] (1) is synthesized by benzylic C[sbnd]S bond cleavage of L-CH₂Ph ligand (where, L-CH₂Ph = 2-(benzylthio)-N-(pyridin-2-ylmethylene)aniline). The complex is thoroughly characterized by several spectroscopic techniques. Geometry of the complex is confirmed by single crystal X-ray crystallography. Electronic structure, redox properties, absorption and emission properties of the complex were studied. DFT and TDDFT calculations were carried out to interpret the electronic structure and absorption properties of the complex respectively. The synthesized Rh(III) complex was tested as catalyst towards transfer hydrogenation reaction of ketones in ⁱPrOH and an excellent catalytic conversion was observed under mild conditions.

Full text of DOI:10.1016/j.ica.2020.120096

Inorganica Chimica Acta 515 (2021) 120096
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
–
Synthesis of new rhodium(III) complex by benzylic C S bond cleavage of
thioether containing NNS donor Schiff base ligand: Investigation of
catalytic activity towards transfer hydrogenation of ketones
Sujan Biswas, Chandan Kumar Manna, Rahul Naskar, Akash Das, Tapan Kumar Mondal*
Inorganic Chemistry Section, Department of Chemistry, Jadavpur University, Kolkata 700032, India
A R T I C L E I N F O
A B S T R A C T
Keywords:
A new rhodium(III)-triphenylphosphine mixed ligand complex, [Rh(PPh3)(L)Cl2] (1) is synthesized by benzylic
Rhodium(III) complex
–
C
S bond cleavage of L-CH2Ph ligand (where, L-CH2Ph = 2-(benzylthio)-N-(pyridin-2-ylmethylene)aniline). The
–
C
S bond cleavage
complex is thoroughly characterized by several spectroscopic techniques. Geometry of the complex is confirmed
by single crystal X-ray crystallography. Electronic structure, redox properties, absorption and emission properties
of the complex were studied. DFT and TDDFT calculations were carried out to interpret the electronic structure
and absorption properties of the complex respectively. The synthesized Rh(III) complex was tested as catalyst
towards transfer hydrogenation reaction of ketones in iPrOH and an excellent catalytic conversion was observed
under mild conditions.
Electrochemistry
Transfer hydrogenation of ketones
DFT computation
1. Introduction
triphenylphosphine complex supported by a tridentate pyridine-imine-
–
thiolato ligand backbone via benzylic C S bond cleavage of the thio-
–
It is well-known that C S bonds can be activated by transition
metals to form novel sulfur compounds or sulfide complexes [1–3] and
this process is extensively studied for the last few decades due to its
ether ligand, L-CH2Ph (where, L-CH2Ph = 2-(benzylthio)-N-(pyridin-2-
ylmethylene)aniline). It’s worth to mention here that the benzylic group
–
plays an important role to cleavage of the C S bond for the present case.
–
S
–
importance in industry [4–6]. Recently, transition-metal mediated C
In our previous work, no C S bond scission was observed and a S(Me)-
bond activation and cleavage is applied in diverse bioorganic and syn-
Rh coordination mode was found under the similar reaction conditions
[21].
–
thetic chemistry [7,8]. Moreover, transition metals mediated C S bond
activation along with the transformation processes are of stimulating
interest from the perspective of synthetic, mechanistic as well as cata-
lytic aspects [9–11]. Transition metal mediated cleavage of both C(aryl)-
S and C(alkyl)-S bonds are extensively studied. Hanton et al. reported Cl-
triggered facile C(alkyl)-S cleavage of thioether moiety in platinum(II)
complex [12]. Goswami et al. reported the effect of reaction temperature
On the other hand, transfer hydrogenation of ketone to the corre-
sponding alcohol is one of the most important fundamental subjects in
modern synthetic chemistry [22,23] and is a convenient method to
reduce carbonyl compounds without the use of hazardous hydrogen gas
or moisture-sensitive hydride reagents [24–27]. Moreover, the transfer
hydrogenation of ketones is widely accepted in industry as a cost-
effective way for the production of a number of hydroxylated organic
products [28]. Over the last few decades, significant effort on hydro-
genation is given on the use of ruthenium, rhodium and iridium catalysts
[29–31]. In view of the significant contribution of rhodium complexes
towards catalysis, herein we have also explored the catalytic efficiency
of the synthesized Rh(III) complex, [Rh(PPh3)(L)Cl2] (1) towards
transfer hydrogenation of ketones in iPrOH.
–
and dπ(M) → π(N N) on C(alkyl)-S cleavage in platinum(II)-thioether
–
complex [13]. Pramanik et al. explored the C(alkyl)-S cleavage in Rh
(III) and Ir(III) complexes in presence of excess PPh3 [14,15]. In recent
years, Biswas et al. reported the activation of both C(aryl)-S and C
(alkyl)-S bonds to form cyclometalates and metal-thiolato complexes
respectively of group 9 metals [16]. In our previous works, we have
reported the synthesis of Pd(II), Ru(II) and Rh(III) complexes by metal
induced C(alkyl)-S and C(aryl)-S bond scission of thioether containing
ligand systems [17–20]. Herein, we have synthesized a new Rh(III)-
* Corresponding author.
E-mail address: tapank.mondal@jadavpuruniversity.in (T. Kumar Mondal).
https://doi.org/10.1016/j.ica.2020.120096
Received 17 July 2020; Received in revised form 18 October 2020; Accepted 19 October 2020
Available online 22 October 2020
0020-1693/© 2020 Elsevier B.V. All rights reserved.

S. Biswas et al.
Inorganica Chimica Acta 515 (2021) 120096
2. Experimental
Table 1
Crystallographic data for [Rh(PPh3)(L)Cl2] (1).
2.1. Materials
Formula
C30H24Cl2N2PRhS
Formula Weight
Crystal System
Space group
a / Å
649.35
2-(Benzylthio)-N-(pyridin-2-ylmethylene)aniline (L-CH2Ph) was
synthesized following the published procedure [32]. Pyridine-2-
carboxaldehyde, 2-aminothiophenol and RhCl3⋅3H2O were purchased
from Sigma Aldrich, and used as received. All other chemicals and sol-
vents were of reagent grade and were used without further purification.
Monoclinic
C2/c
33.096(3)
11.0554(8)
17.9101(14)
114.662(4)
5955.4(8)
8
b / Å
c / Å
β (◦)
V / Å3
Z
2.2. Physical measurements
ρcalcd / g cmꢀ 3
1.448
μ
/ mmꢀ 1
0.898
Microanalyses (C, H, N) were performed using a Perkin-Elmer CHN-
2400 elemental analyzer. Electronic spectra were measured on Lambda
750 PerkinElmer spectrophotometer in dichloromethane solution. IR
spectra were recorded on RX-1 Perkin Elmer spectrophotometer in the
spectral range 4000–400 cmꢀ 1 with the samples in the form of KBr
pellets. Luminescence property was measured using Shimadzu RF-6000
fluorescence spectrophotometer at room temperature (298 K) in aceto-
nitrile solution by 1 cm path length quartz cell. Fluorescence lifetimes
were 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 [33]. The goodness of fit was evaluated by χ2
criterion and visual inspection of the residuals of the fitted function to
the data. 1H NMR spectra were recorded in CDCl3 on Bruker 300 MHz
FT-NMR spectrometers in presence of TMS as internal standard. Cyclic
voltammograms were recorded using 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. Tetrabutylammonium hexafluorophosphate (NBu4PF6)
(0.1 M) was used as the supporting electrolyte and the scan rate used
was 50 mV sꢀ 1 in CH2Cl2 under N2 atmosphere. ESI mass spectra were
recorded on a micro mass Q-TOF mass spectrometer. The one electron
oxidized species 1þ was generated by exhaustive electrolysis of 1 [34].
The 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, maintaining nearly
equal absorbance (~0.1), and the emission spectra were recorded. The
area of the emission spectrum was integrated using the software avail-
able in the instrument and the quantum yield is calculated according to
the following equation:
T / K
293(2)
Radiation / Å
hkl range
0.71073
ꢀ 42 to 42; ꢀ 14 to 14; –23 to 23
2624
F(000)
θ range (◦)
Reflection collected
1.963–27.546
49,862
Unique reflns (Rint
)
6864
Observed data (I > 2
σ
(I))
6044
Data/restraints/parameters
6864 / 0 / 334
0.0238, 0.0593
1.034
R1a,wR2b[I > 2
σ(I)]
GOFc
Largest diff. Peak/hole, / e Å─3
0.543 and ꢀ 0.489
∑
∑
a
R1
=
|(|Fo| – |Fc|)| /
|Fo|.
∑
∑
wR2 = {
[w (F2o–F2c)2] /
[w (F2o)2] }1/2, w = 1/[σ2(F2o) + (0.0303P)2
+
b
5.6657P], where P = (F2o + 2Fc2)/3.
∑
GOF = { [w(F2o–Fc2)2] / (n–p)}1/2 , where n = number of measured data and
c
p = number of parameters.
ethyl acetate-petroleum ether mixture. After removal of the solvent
under reduced pressure, the solid pure green product was further dried
under vacuum. Yield, 0.155 g (63%).
Anal. Calc. for C30H24N2Cl2PRhS: Calculated C, 55.49; H, 3.37; N,
4.31 Found: C, 55.35; H, 3.65; N, 4.55. IR (KBr, υmax/cmꢀ 1): 1584
1
–
–
(C N), 747 (S C). H NMR (CDCl3, ppm): 8.78 (1H, s, CH = N), 8.66
–
(1H, d, J = 4.4 Hz), 8.43 (1H, d, J = 8.2 Hz), 7.83 (1H, m), 7.12–7.52
(20H, m). ESI-MS (m/z) calculated for C30H24N2ClPRhS [Mꢀ Cl]+
613.0141, found 613.0157. 13C{ H} NMR (CDCl , ppm): 171.2 (C N),
1
–
–
3
152.1 (Ar-C), 148.3 (Ar-C), 146.4 (Ar-C), 138.3 (PPh3-C), 132.4 (PPh3-
CH), 129.4 (PPh3-CH), 126.3 (Ar-C), 123.8 (Ar-C). 31P{1H} NMR
(CDCl3, ppm): 29.7 (d, 1JRhꢀ P = 116.8 Hz, PPh3). UV–Vis (in CH2Cl2),
λmax
(
ε
, Mꢀ 1cmꢀ 1): 650 (1230), 333 (8751), 267 (25328). E1/2 : 0.68 V
(ΔE = 88 mV) (Epa: 0.724 V Epc: 0.636 V); Epc: ꢀ 1.09 V.
ϕS/ϕR = [AS / AR ] × [(Abs)R /(Abs)S ] × [ηS2
/
ηR2
]
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 so-
lution 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.
2.4. Procedure for catalytic transfer hydrogenation
In a typical experiment the ketone (2 mmol), KOH (0.02 mmol), and
complex 1 (0.005 mmol) were added to degassed iPrOH (5 mL), and the
mixture was stirred at 80 ◦C in an inert atmosphere for 6 h. The reaction
was then monitored at various time intervals by the use of GC. After the
reaction was complete, iPrOH was removed on a rotary evaporator, and
the resulting semisolid was extracted with diethyl ether (5 × 5 mL). The
combined liquid phase was analyzed by GC using undecane as an in-
ternal standard.
The yields of catalytic conversion 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
μ
m film thickness. The column,
◦
injector and detector temperatures were 200, 250 and 250 C respec-
tively. The carrier gas was N2 (UHP grade) at a flow rate of 30 mL/min.
The injection volume of sample was 2 μL. The oxidation products were
2.5. Computational Details
identified by GC co-injection with authentic samples.
Full geometry optimization of complex 1 was carried out by DFT/
B3LYP method [35,36]. All elements except rhodium were assigned the
6-31G(d) basis set. For Rh, LanL2DZ basis set with effective core po-
tential was employed [37–39]. The vibrational frequency calculation
was performed to ensure that the optimized geometry represents the
local minima and there are only positive eigenvalues. All calculations
were performed with Gaussian09 program package [40] with the aid of
the GaussView visualization program. Vertical electronic excitations
based on B3LYP optimized geometry were computed using the time-
2.3. Preparation of [Rh(PPh3)(L)Cl2] (1)
The reaction mixture containing RhCl3⋅3H2O (0.10 g, 0.38 mmol), L-
CH2Ph (0.101 g, 0.38 mmol) and PPh3 (0.262 g, 1 mmol) in 20 mL
acetonitrile was refluxed for 8 h to yield a deep green solution. The
solvent was then removed under reduced pressure. The dried crude
product was purified by using silica gel (mesh 60–120) column chro-
matography. The green band of the complex was eluted by 30% (v/v)
2

S. Biswas et al.
Inorganica Chimica Acta 515 (2021) 120096
Scheme 1. Synthesis of complex 1 with L-CH2Ph ligand (where, L-CH2Ph = 2-
(benzylthio)-N-(pyridin-2-ylmethylene)aniline).
dependent density functional theory (TDDFT) formalism [41–43] in
CH2Cl2 using conductor-like polarizable continuum model (CPCM)
[44–46]. The fractional contributions of various groups to each molec-
ular orbital was calculated using GaussSum program [47].
Fig. 1. UV–vis-NIR spectra of complex 1 and electrogenerated complex 1þ
in CH2Cl2.
2.6. Crystal structure determination and refinement
Details of crystal analysis, data collection and structure refinement
data for [Rh(PPh3)(L)Cl2] (1) is given in Table 1. Single crystal data
collections were performed with an automated Bruker SMART APEX
CCD diffractometer using graphite monochromatized Mo-Kα radiation
(λ = 0.71073 Å) at 293 ◦C. Reflection data were recorded using the
ω
scan technique. The data were integrated using the SAINT [48] program,
and the absorption corrections were made with SADABS [48]. The
structure was solved by direct method and refined by full-matrix least-
squares techniques on F2 using the SHELXL-2016/6 program [49]. All
data were corrected for Lorentz and polarization effects, and the non-
hydrogen atoms were refined anisotropically. Hydrogen atoms were
included in the refinement process as per the riding model. The electron
density map also showed the presence of some unassignable peaks,
which were removed by SQUEEZE method [50].
3. Results and discussion
3.1. Synthesis and spectral characterization
The Rh(III)-phosphine complex, [Rh(PPh3)(L)Cl2] (1) was synthe-
sized by the reaction of RhCl3, 2-(benzylthio)-N-(pyridine-2-ylmethy-
lene)aniline (L-CH2Ph) and excess PPh3 in acetonitrile under refluxing
condition (scheme 1). The colour of the reaction mixture was changed
Fig. 2. Luminescence spectrum of 1 in CH2Cl2 (λex = 333 nm).
–
from red to green. In the course of the reaction benzylic C S bond of
thioether containing L-CH2Ph ligand is cleaved and L binds to the
rhodium(III) centre using pyridyl-N, imine-N and thiophenolato-S
atoms. The complex was thoroughly characterized by several spectro-
scopic techniques. In IR spectra, the free ligand (L-CH2Ph) stretching at
1621 cmꢀ 1 and 776 cmꢀ 1 corresponding to imine
υ
–
–
(C N) and υ(C S)
–
are shifted to 1584 cmꢀ 1 and 747 cmꢀ 1 in the complex supporting the
coordination of the ligand to the metal. The 1H NMR peak at 4.16 ppm
corresponding to benzylic protons (–CH2) is absent in metal complex
–
indicating the C S bond cleavage (experimental section). The singlet
peak corresponding to imine proton (HC = N) appears at 8.78 ppm.
Aromatic protons appeared as multiplet due to the presence of PPh3
group. The overlapping of many proton resonances due to their similar
chemical shifts has prevented identification of individual proton signals
of the aromatic protons; though the spectra shows the calculated num-
ber of equivalent aromatic protons.
The solution spectrum of the rhodium(III) complex, [Rh(PPh3)(L)
Cl2] (1) in dichloromethane exhibits low energy peak at 650 nm (
ε
,
,
1230 Mꢀ 1cmꢀ 1) along with two moderately intense bands at 333 (
ε
Fig. 3. Exponential decay profile of 1 in CH2Cl2 (τ = 1.57 ns).
3

S. Biswas et al.
Inorganica Chimica Acta 515 (2021) 120096
Table 2
X-ray and calculated bond distances (Å) and angles (◦) of 1 and 1þ.
Bond (Å)
X-ray
Calc.
1
1
1þ
Rh1-Cl1
2.3521(5)
2.4353(5)
2.3054(5)
2.2902(5)
2.1076(15)
2.0001(14)
2.412
2.433
2.367
2.413
2.141
2.041
2.383
2.473
2.317
2.416
2.102
2.047
Rh1-Cl2
Rh1-S1
Rh1-P1
Rh1-N1
Rh1-N2
Angles (◦)
N1- Rh1- N2
N1-Rh1- P1
N1- Rh1- S1
N1- Rh1-Cl1
N1- Rh1-Cl2
N2-Rh1- P1
N2- Rh1- S1
N2- Rh1-Cl1
N2- Rh1-Cl2
P1-Rh1- S1
P1-Rh1-Cl1
P1-Rh1-Cl2
S1-Rh1-Cl1
S1-Rh1-Cl2
Cl1- Rh1-Cl2
79.99(6)
79.964
96.059
165.034
95.391
85.227
95.986
85.523
173.150
84.507
88.992
89.483
178.648
98.728
89.793
90.116
79.963
95.723
161.301
96.493
88.806
95.852
85.442
173.303
84.612
97.345
90.135
175.459
96.790
78.178
89.649
94.57(4)
166.12(4)
97.00(4)
86.53(4)
94.15(4)
86.28(4)
173.25(4)
84.97(4)
88.413(19)
92.109(18)
178.458(18)
96.434(18)
90.27(2)
88.831(19)
Fig. 4. ORTEP plots of 1 with 35% ellipsoidal probability.
8751 Mꢀ 1cmꢀ 1) and 267 nm (
ε
, 25328 Mꢀ 1cmꢀ 1) (Fig. 1). In addition, a
by DFT/B3LYP method. The optimized bond distances and angles are
well correlated with the X-ray crystal structure data in the native state.
Upon oxidation, significant change in Rh1-S1 bond distance is observed
(Table 2).
low energy band as shoulder is also appeared at 479 nm. Upon excitation
at 333 nm, an emission band at 432 nm with emission quantum yield (ϕ)
= 0.015 is observed in CH2Cl2 (Fig. 2). Lifetime data of the complex was
taken at 298 K in CH2Cl2 solution when excited at 370 nm. The fluo-
rescence decay curve was deconvoluted with respect to the lamp profile.
The observed florescence decay fits with bi-exponential nature (Fig. 3).
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 fluorescence lifetime of the complex is
found to be 1.57 ns.
The energy and compositions of selected molecular orbitals of 1 are
summarized in Table 3. Contour plots of selected molecular orbitals are
shown in Fig. 6. The higher energy occupied molecular orbital (HOMO)
has 90% contribution of L (S, 53%) along with reduced contribution
(06%) of d
π
(Rh). The HOMO-1 to HOMO-4 have major contribution of
(Rh)
*(L) character
(Rh)
p
π
(Cl) orbitals (61–89%) along with significant contribution of d
π
orbitals. The low lying virtual orbital, LUMO has 95%
π
while LUMO + 1 and LUMO + 2 have significant contribution of d
π
orbitals. The HOMO to LUMO energy gap in the complex is found to be
2.23 eV.
3.2. Molecular structure
To understand the electronic structure in the oxidized state (1þ), we
have considered the effect in changes in the energies and compositions
of molecular orbitals of the complex in the oxidized form. Energy and
composition of selected molecular orbitals are summarized in Table S1
Single crystals of 1 were grown by layering n-hexane and dichloro-
methane solution of the complex. Selected bond distances and bond
angles of the complex are summarized in Table 2. The molecular
structure with atomic numbering is represented in Fig. 4. After cleavage
of benzyl fragment, the uninegative ligand binds in a tridentate fashion
through pyridyl-N, imine-N and thiophenolato-S atoms to the rhodium
(III) center. The geometry about rhodium(III) is significantly deviated
from ideal octahedron. The deviation of coordination sphere from ideal
octahedron is reflected from small bite angles of the five membered
chelate rings, Rh1-N1-C5-C6-N2, 79.99(6)◦ and Rh1-N2-C7-C8-S1,
86.28(4)◦. The Rh-N(pyridyl) bond, Rh1-N1, 2.1076(15) Å is much
more elongated than the Rh-N(imine) bond distance, Rh1-N2, 2.0001
(14) Å, while the reverse Re-N bond distances was reported previously
[51]. The Rh1-S1 bond distance, 2.3054(5) Å is comparable to the re-
ported Rh-S bond distances [52–54]. Rh1-Cl1 and Rh1-Cl2 bond lengths
are found to be 2.3521(5) and 2.4353(5) Å respectively. A 2D supra-
and Table S2 for
α and β spin respectively. The contour plots of selected
molecular orbitals are shown in Fig. S1 and Fig. S2 for
α and β spin
respectively. The Spin density of the oxidized species is well distributed
on the ligand with major contribution of S atom (63%) (Fig. 7).
3.4. TDDFT calculation and electronic spectra
The solution spectrum of 1 in dichloromethane exhibits peaks at 650
nm (
ε
, 1230 Mꢀ 1cmꢀ 1) along with a sloulder at 479 nm. In addition, two
moderately intense bands at 333 (
ε
, 8751 Mꢀ 1cmꢀ 1) and 267 nm (
ε,
25328 Mꢀ 1cmꢀ 1) are observed (Fig. 1). To interpret the electronic
transitions in the complex, TDDFT calculation was carried out by
TDDFT/CPCM method in dichloromethane. The band at 650 nm corre-
sponds to the HOMO → LUMO transition (λ = 666 nm; f = 0.034) having
ILCT character (Table 4). The peak appeared as shoulder at 479 nm has
mixed XLCT (halogen to ligand charge transfer transition) and MLCT
(metal to ligand charge transfer transitions) character. The high energy
molecular structure is formed by inter-molecular π… π interactions be-
tween phenyl ring (Cg(4): C7-C8-C9-C10-C11-C12) and pyridyl ring (Cg
(3): N1-C1-C2-C3-C4-C5) of the adjacent molecule with Cg-Cg distance
of 3.7462(14) Å. In addition, strong intra-molecular π… π interactions
are found between phenyl ring of the ligand (Cg(4)) and one of the
phenyl ring of PPh3 (Cg(5): C13-C14-C15-C16-C17-C18) with Cg-Cg
distance of 3.7527(14) Å (Fig. 5).
band at 333 nm corresponds to the
complex.
π(L) → π*(L) transition (ILCT) in the
3.3. DFT calculation and electronic structure
3.5. Electrochemistry
The geometry of the 1 and the oxidized form, 1þ were optimized to
The electrochemical behavior of the complex was investigated by
interpret the electronic structures in native as well as in the oxidized sate
cyclic voltammetry (CV) in dichloromethane solvent using tetra-n-
4

S. Biswas et al.
Inorganica Chimica Acta 515 (2021) 120096
Fig. 5. 2D-supramolecular structure of 1 by intra- and inter-molecular π… π interactions.
Table 3
Energy and composition of selected molecular orbitals of 1.
MO
Energy (eV)
% of composition
L
∑
Cl
Rh
PPh3
LUMO þ 5
LUMO þ 4
LUMO þ 3
LUMO þ 2
LUMO þ 1
LUMO
ꢀ 0.77
ꢀ 0.89
ꢀ 1.37
ꢀ 1.52
ꢀ 1.77
ꢀ 2.80
ꢀ 5.03
ꢀ 5.81
ꢀ 5.83
ꢀ 5.98
ꢀ 6.10
ꢀ 6.63
ꢀ 6.71
ꢀ 6.79
ꢀ 6.92
ꢀ 7.11
ꢀ 7.20
05
02
0
04
0
89
96
05
01
33
01
02
01
02
10
02
12
57
93
75
90
21
04
86
02
09
20
01
02
84
89
70
61
07
17
02
09
02
20
07
44
37
03
06
11
08
17
25
07
06
01
05
02
14
46
09
95
HOMO
90(S, 53)
04
HOMO-1
HOMO-2
HOMO-3
HOMO-4
HOMO-5
HOMO-6
HOMO-7
HOMO-8
HOMO-9
HOMO-10
01
03
12
74
20
04
11
06
45
butylammonium hexafluorophosphate (NBu4PF6) (0.1 M) as supporting
electrolyte and a Ag/AgCl reference electrode. The complex exhibits a
reversible oxidation couple with E1/2, 0.68 V (ΔE = 88 mV) along with
an irreversible reduction peak at ꢀ 1.09 V in the potential range of ꢀ 1.5
to 1.0 V versus Ag/AgCl electrode (Fig. 8). The oxidation couple may be
assigned to Rh(III)/Rh(IV) oxidation in the complex [55,56]. But the
composition of HOMO of the complex has 90% ligand character with
oxidation is assigned as thiophenolato to thiyl radical formation over the
minor possibility of Rh(III)/Rh(IV) process in the complex. The elec-
tronically generated oxidized species by extensive bulk electrolysis at
constant potential at 0.7 V exhibits sharp changes in the UV–VIS-NIR
spectra. The low energy band at 655 nm in the native state is red shifted
and observed at 766 nm. In addition, a new band at 564 nm is developed
during oxidation (Fig. 1).
major contribution of pπ(S) orbitals (53%). So, we may consider the
ligand centered oxidation on thiophenolato-S to form thiyl radical in the
complex [14,15,17]. The irreversible cathodic peak at ꢀ 1.09 V may
corresponds to the reduction of coordinated ligand (L) as the composi-
3.6. Catalytic transfer hydrogenation reactions
Rhodium complex mediated transfer hydrogenation reactions are
discovered to be very effective catalytic systems in which hydrogen is
transferred from one organic molecule to another molecule. The present
Rh(III) complex 1 was taken as catalyst and the catalytic activity in
transfer hydrogenation of different aromatic and aliphatic ketones in
presence of iPrOH and KOH as promoter was carried out.
tion of LUMO has 95% π*(L) character in the complex.
Moreover, for better understand the oxidation process in the com-
plex, we have calculated the Mulliken atomic charges by DFT/B3LYP
method of 1 and 1þ (Table 5). Mulliken atomic charges of 1 and 1þ
species clearly show that there is significant enhancement of positive
charge on S atom compared to rhodium atom in 1þ. Again, the possi-
bility of formation of thiyl radical is further supported by the 63% spin
density on S atom in comparison to 3% on rhodium in 1þ (Fig. 7). So, the
The transfer hydrogenation of acetophenone was standardized with
the variation of base, catalyst loading, reaction time, temperature and
results are summarized in Table 6. When the amount of catalyst
5

S. Biswas et al.
Inorganica Chimica Acta 515 (2021) 120096
Fig. 6. Contour plots of some selected molecular orbitals of 1. Isodensity value 0.04 e Bohr-3.
Fig. 8. Cyclic voltammogram of 1 in in CH2Cl2 with respect to Ag/AgCl
reference electrode ([NBu4PF6] was used as the supporting electrolyte).
Table 5
Mulliken atomic charges calculated by DFT/B3LYP method of 1 and 1þ.
Fig. 7. Spin density plot of 1þ (Rh, 3%; S, 63%). Isodensity value 0.004 e
Atoms
1
1þ
Bohr-3.
Rh1
Cl1
Cl2
P1
ꢀ 0.301
ꢀ 0.275
ꢀ 0.245
0.694
ꢀ 0.352
ꢀ 0.190
ꢀ 0.148
0.707
S1
0.109
0.366
N1
N2
ꢀ 0.471
ꢀ 0.501
ꢀ 0.495
ꢀ 0.514
Table 4
Vertical electronic excitations calculated by TDDFT/CPCM method of 1 in
CH2Cl2.
Eexcitation
(eV)
λexcitation
Osc.
Key
Character
λexpt.
increased from 0.10 to 0.15, 0.20 and 0.25 mol%, the yields of 1-phenyl-
ethyl alcohol were increased from 72 to 85, 94 and 98% respectively.
Further, the reaction was carried out in absence of catalyst 1 and with
RhCl3. In both the cases no significant catalytic conversions were
observed. With the increase of reaction time from 1 to 6 h, the yield was
increased from 51 to 98%. Reaction time was also played a vital role,
with the increase of temperature from 40 to 80 ◦C the yields of 1-phenyl-
ethyl alcohol increased from 25 to 98%. The bases play a significant role
in transfer hydrogenation reaction and without any base the reaction
was hardly proceeded. In the catalytic cycle, probably the Rh-Cl bond is
(nm)
Strength
(f)
transitions
(nm)
1.8612
2.6106
3.4942
666.2
0.0343
0.0113
0.0781
(98%)
p
π
(S) →
π*(L)
655
479
333
HOMO →
LUMO
ILCT
474.92
354.83
(86%)
p
π
(Cl)/d
*(L)
XLCT/MLCT
(L) → *(L),
ILCT
π
(Rh)
HOMO-3 →
LUMO
→
π
(75%)
π
π
HOMO-5 →
LUMO
6

S. Biswas et al.
Inorganica Chimica Acta 515 (2021) 120096
Table 6
Table 7
Optimization of transfer hydrogenation of acetophenonea by complex 1.
Transfer hydrogenation of various ketones using complex 1.a
Entry
Amount of
Base
used
Amount of
Temp.
Time
(h)
Yield
Entry
1
Ketones
Alcohols
Conversion
TONc
392
cat. (mol%)
base (mol%)
(◦C)
(%)b
(%)b
1
0.10
0.15
0.20
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
KOH
KOH
KOH
KOH
Na2CO3
NaOAc
KOtBu
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0.5
0.8
1.0
1.0
1.0
1.0
1.0
1.0
1.0
80
80
80
80
80
80
80
80
80
40
60
80
80
80
80
80
6
6
6
6
6
6
6
6
6
6
6
1
2
3
4
5
72
85
94
98
73
45
82
79
92
25
54
51
72
81
88
95
98
2
3
4
5
6
2
3
92
94
368
376
7
8
9
10
11
12
13
14
15
16
4
5
96
93
384
372
a
Reaction condition: acetophenone (2 mmol), iPrOH 5 mL).
b
Conversions were determined by GC with undecane as an internal standard
and were reported mean values of three runs.
cleaved and formation of new intermediate complex having Rh-H bond
is taking place which is then effectively reduced the ketones to their
corresponding alcohols [31]. In general, the catalytic conversion of
transfer hydrogenation reactions is strongly dependent on the base
strength – the stronger the bases higher the yields [57–59]. In present
case, reaction was proceeded very well with strong base (KOH), while
for weak bases like Na2CO3 and NaOAc, the yields were very poor.
In recent years we have successfully synthesized several rhodium
(III)-triphenylphospine complexes and explored their catalytic effi-
ciency towards transfer hydrogenation of ketones, a moderate to high
catalytic conversions (85–98%) were observed under optimum reaction
conditions [19–21]. Kühn et al. observed 86–100% yields for hetero-
cyclic carbine rhodium(I) complexes [60]. Karakas¸ and co-workers used
ionic liquid based R(I) complexes as efficient catalysts and observed
90–99% yields [61]. The results of transfer hydrogenation by the present
Rh(III) complex 1 under are summarized in Table 7. For aliphatic ke-
tones like 2-butanone, cyclopentanone, cyclohexanone, cycloheptanone
and cyclooctanone the converstions to their corresponding alcohols
were achieved to 89–96%. While for aromatic ketones with electron
donating or withdrawing groups excellent yields were observed
(96–98%).
6
7
89
97
356
388
8
9
98
96
392
384
10
98
392
4. Conclusion
a
Reaction conditions: ketone (2 mmol), Rh(III) complex (0.25 mol%), KOH
(1.0 mol%), iPrOH (5 mL), temperature: 80 ◦C; bConversions were determined
by GC with undecane as an internal standard and were reported mean values of
three runs; cTurnover number (TON) = mole of product/mol of catalyst.
Herein, we have synthesized new rhodium(III) complex, [Rh(L)
–
(PPh3)Cl2] (1) by C S bond cleavage of thioether containg ligand, L-
CH2Ph. The complex is thoroughly characterized by several spectro-
scopic techniques and the distorted octahedral geometry is confirmed by
single crystal X-ray study. The complex exhibits ligand based thio-
phenolato to thiyl radical oxidation over the alternate possibility of Rh
(III)/Rh(IV) process. The complex effectively catalyzed the transfer
hydrogenation reaction of ketones with moderate to high yields
CRediT authorship contribution statement
Sujan Biswas: Investigation, Writing - original draft. Chandan
Kumar Manna: Investigation. Rahul Naskar: Investigation. Akash
Das: Investigation. Tapan Kumar Mondal: Supervision, Writing - re-
view & editing.
i
(89–98%) in PrOH. Electronic structure, solution spectrum and redox
properties are well interpreted by DFT and TDDFT calculations.
7

S. Biswas et al.
Inorganica Chimica Acta 515 (2021) 120096
[20] P. Roy, C.K. Manna, R. Naskar, T.K. Mondal, Synthesis of a rhodium(III)
triphenylphosphine complex via Cꢀ S bond cleavage of an azo-thioether ligand: X-
ray structure, electrochemistry and catalysis towards transfer hydrogenation of
ketones, Polyhedron 158 (2019) 208–214.
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
[21] S. Biswas, D. Sarkar, S. Kundu, P. Roy, T.K. Mondal, Rhodium(III)-
triphenylphosphine complex with NNS donor thioether containing Schiff base
ligand: synthesis, spectra, electrochemistry and catalytic activity, J. Mol. Struct.
1099 (2015) 297–303.
Acknowledgment
[22] D. Wang, D. Astruc, The golden age of transfer hydrogenation, Chem. Rev. 115
(2015) 6621–6686.
[23] M. Yoshimura, S. Tanaka, M. Kitamura, Recent topics in catalytic asymmetric
hydrogenation of ketones, Tetrahedron Lett. 55 (2014) 3635–3640.
[24] J. Ito, H. Nishiyama, Recent topics of transfer hydrogenation, Tetrahedron Lett. 55
(2014) 3133–3146.
Financial support received from the Science and Engineering
Research Board (SERB) (No. EEQ/2018/000266), New Delhi, India is
gratefully acknowledged. TKM is also grateful to RUSA II programme for
financial support. S. Biswas and R. Naskar are thankful to UGC, New
Delhi, India for fellowship.
[25] R. Malacea, R. Poli, E. Manoury, Asymmetric hydrosilylation, transfer
hydrogenation and hydrogenation of ketones catalyzed by iridium complexes,
Coord. Chem. Rev. 254 (2010) 729–752.
[26] T. Ikariya, A.J. Blacker, Asymmetric transfer hydrogenation of ketones with
bifunctional transition metal-based molecular catalysts, Acc. Chem. Res. 40 (2007)
1300–1308.
Appendix A. Supplementary data
¨
[27] J.S.M. Samec, J.E. Backvall, P.G. Andersson, P. Brandt, Mechanistic aspects of
transition metal-catalyzed hydrogen transfer reactions, Chem. Soc. Rev. 35 (2006)
237–248.
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.ica.2020.120096.
[28] J. Magano, J.R. Dunetz, Large-scale carbonyl reductions in the pharmaceutical
industry, Org. Process Res. Dev. 16 (2012) 1156–1184.
[29] X.-H. Zhu, L.-H. Cai, C.-X. Wang, Y.-N. Wang, X.-Q. Guo, X.-F. Hou, Efficient and
versatile transfer hydrogenation catalysts: Iridium (III) and ruthenium (II)
complexes with 4-acetylbenzyl-N-heterocyclic carbenes, J. Mol. Catal. A Chem.
393 (2014) 134–141.
References
[1] T.-Y. Luh, C.-F. Lee, Dithioacetals as zwitterion synthons, Eur. J. Org. Chem.
3875–3885 (2005).
[30] B. He, P. Phansavath, V. Ratovelomanana-Vidal, Rhodium-catalyzed asymmetric
transfer hydrogenation of 4-quinolone derivatives, Org. Chem. Front. 2 (2020)
975–979.
[2] I.P. Beletskaya, V.P. Ananikov, Transition-metal-catalyzed Cꢀ S, Cꢀ Se, and Cꢀ Te
bond formation via cross-coupling and atom-economic addition reactions, Chem.
Rev. 111 (2011) 1596–1636.
[31] O. Prakash, P. Singh, G. Mukherjee, A.K. Singh, Efficient catalysis of transfer
hydrogenation of ketones and oxidation of alcohols with newly designed half-
sandwich rhodium(III) and iridium(III) complexes of half-pincer chalcogenated
pyridines, Organometallics 31 (2012) 3379–3388.
[3] L. Wang, W. He, Z. Yu, Transition-metal mediated carbon–sulfur bond activation
and transformations, Chem. Soc. Rev. 42 (2013) 599–621.
[4] R. Tan, D. Song, Cꢀ H and Cꢀ S activations of quinoline-functionalized thiophenes
by platinum complexes, Organometallics 30 (2011) 1637–1645.
[5] S. Kundu, W.W. Brennessel, W.D. Jones, C-S bond activation of thioesters using
platinum(0), Organometallics 30 (2011) 5147–5154.
˜
[32] P. Pattanayak, D. Patra, P. Brandao, D. Mal, V. Felix, Synthesis and
characterization of palladium (II) complex of Schiff base ligand: CS bond cleavage
and catalytic activity, Inorg. Chem. Commun. 53 (2015) 68–71.
[6] M.R. Grochowski, T. Li, W.W. Brennessel, W.D. Jones, Competitive carbonꢀ sulfur
vs carbonꢀ carbon bond activation of 2-cyanothiophene with [Ni(dippe)H]2, J. Am.
Chem. Soc. 132 (2010) 12412–12421.
[33] B. Valuer, Molecular Fluorescence: Principles and Applications, Wiley-VCH,
Weinheim, 2001.
[34] N.D. Paul, S. Samanta, T.K. Mondal, S. Goswami, Examples of reductive azo
cleavage and oxidative azo bond formation on Re2(CO)10 template: isolation and
characterization of Re(III) complexes of new azo-aromatic ligands, Inorg. Chem. 50
(2011) 7886–7893.
[7] Y. Miyazaki, K. Oohora, T. Hayashi, Methane generation via intraprotein C-S bond
cleavage in cytochrome b562 reconstituted with nickel didehydrocorrin,
J. Organomet. Chem. 901 (2019) 120945.
[8] J. Lou, Q. Wang, P. Wu, H. Wang, Y.-G. Zhou, Z. Yu, Transition-metal mediated
carbon–sulfur bond activation and transformations: an update, Chem. Soc. Rev. 49
(2020) 4307–4359.
[35] A.D. Becke, Density-functional thermochemistry. III. The role of exact exchange,
J. Chem. Phys. 98 (1993) 5648–5652.
[36] C. Lee, W. Yang, R.G. Parr, Development of the Colle-Salvetti correlation-energy
formula into a functional of the electron density, Phys. Rev. B 37 (1988) 785–789.
[37] P.J. Hay, W.R. Wadt, Ab initio effective core potentials for molecular calculations.
Potentials for the transition metal atoms Sc to Hg, J. Chem. Phys. 82 (1985)
270–283.
[9] K. Ray, S.D. George, E.I. Solomon, K. Wieghardt, F. Neese, Description of the
ground-state covalencies of the bis(dithiolato) transition-metal complexes from X-
ray absorption spectroscopy and time-dependent density-functional calculations,
Chem. Eur. J. 13 (2007) 2783–2797.
[10] M. Tamura, K. Tsuge, A. Igashira-Kamiyama, T. Konno, Bis(bipyridine)ruthenium
(II) complexes with an aliphatic sulfinato donor: synthesis, characterization, and
properties, Inorg. Chem. 50 (2011) 4764–4771.
[38] W.R. Wadt, P.J. Hay, Ab initio effective core potentials for molecular calculations.
Potentials for main group elements Na to Bi, J. Chem. Phys. 82 (1985) 284–298.
[39] P.J. Hay, W.R. Wadt, Ab initio effective core potentials for molecular calculations.
Potentials for K to Au including the outermost core orbitals, J. Chem. Phys. 82
(1985) 299–310.
[11] S.G. Modha, V.P. Mehta, E. Van der Eycken, Transition metal-catalyzed C-C bond
formation via C–S bond cleavage: an overview, Chem. Soc. Rev. 42 (2013)
5042–5055.
[40] Gaussian 09, Revision D.01, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E.
Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A.
Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J.
Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J.
Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A.
Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K.
N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A.
Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M.
Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L.
Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg,
[12] L.R. Hanton, K. Lee, Cꢀ S bond cleavage by chloride in a thioether N2S2 complex of
platinum, Inorg. Chem. 38 (1999) 1634–1637.
[13] S. Mandal, N. Paul, P. Banerjee, T.K. Mondal, S. Goswami, 1,4-Alkyl migration
associated with simultaneous S-C bond cleavage and N–C bond formation in
platinum complexes of 2-aminothioethers. Characterization of intramolecular
interligand charge transfer phenomenon, Dalton Trans. 39 (2010) 2717–2726.
[14] K. Pramanik, U. Das, B. Adhikary, D. Chopra, H. Stoeckii-Evans, RhCl3-assisted
Cꢀ H and Cꢀ S bond scissions: isomeric self-association of organorhodium(III)
thiolato complex. synthesis, structure, and electrochemistry, Inorg. Chem. 47
(2008) 429–438.
[15] U. Das, T. Ghorui, B. Adhikary, S. Roy, S. Pramanik, K. Pramanik, Iridium-mediated
C-S bond activation and transformation: organoiridium(iii) thioether, thiolato,
sulfinato and thiyl radical compounds. Synthesis, mechanistic, spectral,
electrochemical and theoretical aspects, Dalton Trans. 44 (2015) 8625–8639.
[16] S. Acharya, P. Bandyopadhyay, P. Das, S. Biswas, A.N. Biswas, Alkyl-sulfur versus
aryl-sulfur bond cleavage in tridentate alkylthiophenylazonaphthols by group 9
metal ions, J. Organomet. Chem. 866 (2018) 13–20.
¨
S. Dapprich, A. D. Daniels, O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, and
D. J. Fox, Gaussian, Inc., Wallingford CT (2009).
[41] R. Bauernschmitt, R. Ahlrichs, Treatment of electronic excitations within the
adiabatic approximation of time dependent density functional theory, Chem. Phys.
Lett. 256 (1996) 454–464.
[42] R.E. Stratmann, G.E. Scuseria, M.J. Frisch, An efficient implementation of time-
dependent density-functional theory for the calculation of excitation energies of
large molecules, J. Chem. Phys. 109 (1998) 8218–8224.
[17] S. Biswas, P. Roy, T.K. Mondal, Synthesis of palladium(II) complex with NNS donor
Schiff base ligand via Cꢀ S bond cleavage: X-ray structure, electrochemistry and
DFT computation, J. Mol. Struct. 1142 (2017) 110–115.
[43] M.E. Casida, C. Jamorski, K.C. Casida, D.R. Salahub, Molecular excitation energies
to high-lying bound states from time-dependent density-functional response
theory: characterization and correction of the time-dependent local density
approximation ionization threshold, J. Chem. Phys. 108 (1998) 4439–4449.
[44] V. Barone, M. Cossi, Quantum calculation of molecular energies and energy
gradients in solution by a conductor solvent model, J. Phys. Chem. A 102 (1998)
1995–2001.
[18] P. Roy, D. Sarkar, P. Ghosh, C.K. Manna, N. Murmu, T.K. Mondal, Synthesis of
luminescent rhodium(III) cyclometalated complex by sp2(C)ꢀ S bond activation:
application as catalyst in transfer hydrogenation of ketones and live cell imaging,
J. Mol. Struct. 1204 (2020) 127524.
[19] P. Roy, R. Naskar, C.K. Manna, T.K. Mondal, Synthesis of thiolato bridged dimeric
rhodium(III) triphenylphosphine complex via Cꢀ S bond cleavage: X-ray structure,
DFT computation and catalytic evaluation towards transfer hydrogenation of
ketones, J. Mol. Struct. 1198 (2019) 126932.
[45] M. Cossi, V. Barone, Time-dependent density functional theory for molecules in
liquid solutions, J. Chem. Phys. 115 (2001) 4708–4717.
8

S. Biswas et al.
Inorganica Chimica Acta 515 (2021) 120096
[46] M. Cossi, N. Rega, G. Scalmani, V. Barone, Energies, structures, and electronic
properties of molecules in solution with the C-PCM solvation model, J. Comput.
Chem. 24 (2003) 669–681.
synthesis and photophysical and electrochemical characterization, Polyhedron 95
(2015) 14–23.
[56] T. Vadivel, M. Dhamodaran, S. Kulathooran, S. Kavitha, K. Amirthaganesan,
S. Chandrasekaran, S. Ilayaraja, S. Senguttuvan, Rhodium(III) complexes derived
from complexation of metal with azomethine linkage of chitosan biopolymer Schiff
base ligand: spectral, thermal, morphological and electrochemical studies,
Carbohydr. Res. 487 (2020) 107878.
[47] N.M. O’Boyle, A.L. Tenderholt, K.M. Langner, cclib: a library for package-
independent computational chemistry algorithms, J. Comput. Chem. 29 (2008)
839–845.
[48] SAINT (version 6.02), SADABS (version 2.03); Bruker AXS Inc., Madison, WI
(2002).
[57] H. Türkmen, T. Pape, F.E. Hahn, B. Cetinkaya, Efficient transfer hydrogenation
using iridium and rhodium complexes of benzannulated N-heterocyclic carbenes,
Eur. J. Inorg. Chem. 5418–5423 (2008).
[49] G.M. Sheldrick, A short history of SHELX, Acta Crystallogr. A 64 (2008) 112–122.
[50] A.L. Spek, Single-crystal structure validation with the program PLATON, J. Appl.
Crystallogr. 36 (2003) 7–13.
[58] M. Ramesh, G. Venkatachalam, Half-sandwich (
η
6-p-cymene) ruthenium(II)
[51] M.S. Jana, A.K. Pramanik, S. Kundu, D. Sarkar, T.K. Mondal, fac-Tricarbonyl
rhenium(I) complexes of 2-(alkylthio)-N-((pyridine-2-yl)methylene)benzenamine:
synthesis, spectroscopic characterization, X-ray structure and DFT calculation,
Inorg. Chim. Acta 399 (2013) 138–145.
complexes bearing 5-amino-1-methyl-3-phenylpyrazole Schiff base ligands:
synthesis, structure and catalytic transfer hydrogenation of ketones, J. Organomet.
Chem. 880 (2019) 47–55.
[59] V.R. Landaeta, A.D. Salazar-La Rosa, R.E. Rodriguez-Lugo, Transfer hydrogenation
of ketones catalyzed by iridium-bulky phosphine complexes, Inorg. Chim. Acta 470
(2018) 303–311.
[52] M. Hirotsu, A. Kobayashi, T. Yoshimura, T. Konno, Rhodium(iii) complexes with
thiolate and thioether ligands derived from fac(S)-[Rh(aet)3] (aet = 2-aminoetha-
nethiolate): selective formation, characterization and properties, J. Chem. Soc.,
Dalton Trans. (2002) 878–884.
´
[60] N.B. Jokic, M. Zhang-Presse, S.L.M. Goh, C.S. Straubinger, B. Bechlars, W.
A. Herrmann, F.E. Kühn, Symmetrically bridged bis-N-heterocyclic carbene
rhodium (I) complexes and their catalytic application for transfer hydrogenation
reaction, J. Organomet. Chem. 696 (2011) 3900–3905.
[53] A. Labande, J.-C. Daran, N.J. Long, A.J.P. White, R. Poli, Rhodium(III) and
ruthenium(II) complexes of redox-active, chelating N-heterocyclic carbene/
thioether ligands, New J. Chem. 35 (2011) 2162–2168.
[61] D.E. Karakas¸, F. Durap, A. Baysal, Y.S. Ocak, K. Rafikova, E.Ç. Kaya, A. Zazybin,
H. Temel, C. Kayan, N. Meriç, M. Aydemir, Transfer hydrogenation reaction using
novel ionic liquid based Rh(I)and Ir(III)-phosphinite complexes as catalyst,
J. Organomet. Chem. 824 (2016) 25–32.
[54] D. Sardar, P. Datta, P. Mitra, C. Sinha, Rhodium(III) and iridium(III) complexes of
thioarylazoimidazoles: synthesis, structure, spectral characterization,
electrochemistry and DFT calculation, Polyhedron 29 (2010) 3170–3177.
[55] S.K. Seth, S. Mandal, P. Purkayastha, P. Gupta, Cyclometalated mono and dinuclear
rhodium(III) and iridium(III) complexes with imidazolyl phenanthrolines:
9