Half?Sandwich (η6?p?Cymene) Ruthenium(II) complexes bearing 5?Amino?1?Methyl?3?Phenylpyrazole Schiff base ligands: Synthesis, structure and catalytic transfer hydrogenation of ketones

Article abstract of DOI:10.1016/j.jorganchem.2018.10.029

New (η⁶?p?cymene) ruthenium(II) complexes containing Schiff base ligands of the general composition [RuCl(η⁶?p?cymene)(L_1?3)] have been synthesized. The complexes were characterized by analytical and spectral (FT?IR, UV–Vis, ¹H NMR and ¹³C NMR) methods. The molecular structure of the representative complex [RuCl(η⁶?p?cymene)(L₃)] 6 was determined by single crystal X?ray diffraction studies, revealing a pseudo-octahedral piano stool geometry around ruthenium(II) ion. Further, one of the complexes 6 was screened for their efficiency as a catalyst in the transfer hydrogenation of various ketones to alcohols in the presence of KOH and 2?propanol showed an excellent conversion up to 99%. Under the optimized conditions, the influence of base, reaction temperature and substrate scope was also reported.

Full text of DOI:10.1016/j.jorganchem.2018.10.029

Accepted Manuscript
6
Half‒Sandwich (η ‒p‒Cymene) Ruthenium(II) complexes bearing 5‒Amino‒1‒
Methyl‒3‒Phenylpyrazole Schiff base ligands: Synthesis, structure and catalytic
transfer hydrogenation of ketones
Madhan Ramesh, Galmari Venkatachalam
PII:
S0022-328X(18)30897-0
DOI:
https://doi.org/10.1016/j.jorganchem.2018.10.029
JOM 20614
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 10 October 2018
Revised Date: 23 October 2018
Accepted Date: 30 October 2018
6
Please cite this article as: M. Ramesh, G. Venkatachalam, Half‒Sandwich (η ‒p‒Cymene)
Ruthenium(II) complexes bearing 5‒Amino‒1‒Methyl‒3‒Phenylpyrazole Schiff base ligands: Synthesis,
structure and catalytic transfer hydrogenation of ketones, Journal of Organometallic Chemistry (2018),
doi: https://doi.org/10.1016/j.jorganchem.2018.10.029.
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Graphical abstract

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6
Half
‒
Sandwich (η ‒
p‒
Cymene) Ruthenium(II) Complexes Bearing 5‒Amino‒
1
‒
Methyl
‒
3
‒Phenylpyrazole Schiff base Ligands: Synthesis, Structure and
Catalytic Transfer Hydrogenation of Ketones
*
Madhan Ramesh and Galmari Venkatachalam
PG & Research Department of Chemistry, Government Arts College, Dharmapuri – 636 705,
Tamil Nadu, India. E-mail: gvchem@gmail.com [Dr. G. Venkatachalam]
Abstract
6
New (η ‒p‒cymene) ruthenium(II) complexes containing Schiff base ligands of the
6
general composition [RuCl(η ‒p‒cymene)(L1‒3)] have been synthesized. The complexes were
1
13
characterized by analytical and spectral (FT‒IR, UV‒Vis, H NMR and C NMR) methods. The
6
molecular structure of the representative complex [RuCl(η ‒p‒cymene)(L )] 6 was determined
3
by single crystal X−ray diffraction studies, revealing a pseudo-octahedral piano stool geometry
around ruthenium(II) ion. Further, one of the complexes 6 was screened for their efficiency as a
catalyst in the transfer hydrogenation of various ketones to alcohols in the presence of KOH and
2
‒propanol showed an excellent conversion up to 99%. Under the optimized conditions, the
influence of base, reaction temperature and substrate scope was also reported.
Keywords:
p‒cymene ruthenium(II) complexes; Schiff base ligands; Characterization; Crystal structure;
Catalytic transfer hydrogenation
1

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1
. Introduction
Half-sandwich ruthenium(II) arene complexes offer a versatile platform for the design
and synthesis of novel compounds with potential applications in catalysis and medicinal and
supramolecular chemistry. Particularly, half-sandwich ruthenium(II) Schiff base complexes are
used as highly efficient transition metal homogeneous catalysts for the synthesis of valuable
organic compounds [1‒3]. In the area of metal complexes catalyzed transformations, bidentate
O, N donor based ligands are playing an important role because of their ability to form
complexes with several metals in different oxidation states. Schiff base compounds are useful
chelating ligands which are readily modifiable to allow fine-tuning of steric and electronic
properties of the ruthenium complex [4]. Exploring the reactivity of half-sandwich ruthenium
complexes with Schiff base ligands would therefore be interesting. These ruthenium complexes
have attracted a lot of interest due to their catalytic activity in a wide range of organic reactions
[5‒14]. Since last decade, a variety of half sandwich ruthenium complexes have been extensively
studied in transfer hydrogenation reactions [15]. Under basic conditions and mainly with i‒PrOH
as the solvent, ruthenium(II) complexes bearing arene, PP, NN, NO, or NPN ligands have been
investigated for transfer hydrogenation reactions [16].
Ruthenium complexes are preferable for transfer hydrogenation reaction than those of
rhodium and iridium because of their high activity and lower cost. Among the various ruthenium
complexes, arene ruthenium complexes belong to a well-established family of metal complexes
played an important role in the development of organometallic chemistry. Noyori and co-
workers have documented N-tosylethylenediamine or β-amino alcohol ligands exhibited efficient
catalytic activity in the transfer hydrogenation of ketones and imines [17]. New 2‒(2‒pyridyl‒2‒
ol)‒1,10-phenanthroline based ruthenium complexes have been reported as highly active
2

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o
catalysts for reduction of ketones in the presence of 2-propanol at 80 C [18]. Recently, Ramesh
et al. have reported arene Ru(II) hydrozone complexes as catalysts for transfer hydrogenation
ketones with low catalyst loading in 5 h [19].
Remarkably, Baratta et al. have developed arene-free ruthenium catalysts which are
extremely active in the transfer hydrogenation of acetophenone with NaOH as the base [20].
Ruthenium complexes containing different types of ligands such as arylazo ligands [21], Schiff
base ligands [22] and 2, 2'‒bipyridine ligand [23] are considered to be the most active catalysts
for transfer hydrogenation reaction in the presence of a base. In order to design new
ruthenium(II) complexes with potential catalytic activity in the reduction of ketones, we decided
to synthesize the half-sandwich ruthenium(II) Schiff base complexes.
6
Herein, we report the synthesis of (η ‒p‒cymene) ruthenium(II) complexes containing bi-
dentate Schiff base ligands along with transfer hydrogenation of a series of ketones. The
synthesized complexes have been characterized by elemental analysis and spectroscopy (FT‒IR,
1
13
UV‒Vis, H NMR and C NMR) techniques. The molecular structure of complex 6 was
confirmed by single crystal X‒ray diffraction. Further, one of the half-sandwich ruthenium(II)
Schiff base complexes was employed as catalyst for promoting a variety of ketones to
corresponding secondary alcohols in the presence of 2‒propanol and KOH.
2
. Results and discussion
2
.1. Synthesis and spectroscopic study
The Schiff base ligands (HL −HL ) 1−3 were readily synthesized from the condensation
1
3
of the 5‒amino‒1‒methyl‒3‒phenylpyrazole with corresponding aldehyde and its derivatives
respectively. The orange half-sandwich ruthenium complexes 4−6 were obtained by reaction of
6
[
(η ‒p‒cymene)Ru(µ‒Cl)Cl] with two equivalent Schiff base ligands in the presence of Et N in
2
3
3

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CH
2
Cl
2
under stirring at room temperature for 12 h (Scheme 1). The ruthenium complexes were
isolated as pure complexes by chromatography silica gel using EtOAc/petroleum ether as an
eluent to yield of 60−80%. All the complexes have been characterized by FT‒IR, UV−Vis,
1
13
H NMR and C NMR spectroscopy. The half-sandwich ruthenium complexes are air and
moisture stable, soluble in CHCl , CH Cl , CH CN, C H , DMSO, CH OH and C H OH
3
2
2
3
6
6
3
2
5
solvents.
6
Scheme 1. Synthesis of half sandwich (η ‒p‒cymene) ruthenium(II) Schiff base complexes.
4

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An infrared red spectrum helps in determining the coordination mode of ligand with
–
1
metal ion. The Free ligands 1‒3 exhibit a broad band in the region 3320–3399 cm , which is
characteristic of the ν(OH) functional group [24]. The azomethine ν(C=N) and the ν(C‒O)
–
1
–1
stretching frequencies are assigned in the region around 1612‒1620 cm and 1270‒1296 cm
respectively [24‒27]. Upon coordination the frequencies of the azomethine ν(C=N) stretching
–
1
shift toward lower frequencies at 1600‒1605 cm and phenolic ν(C‒O) stretching exhibit
–
1
slightly higher frequencies at 1320‒1331 cm as compared to their respective ligands. Thus, the
imine nitrogen and phenolic oxygen functionalities suggests the presence of a pseudo octahedral
environment around ruthenium(II) metal centre [28, 29].
The electronic spectra of the half-sandwich ruthenium(II) Schiff base complexes in
chloroform exhibited very intense bands around 300–330 nm and 340–380 nm, which are
assigned to the ligand-centered (LC) π–π* and n–π* transitions, respectively. The representative
UV‒Vis spectra of complexes 4‒6 are given in Fig. 1. The lowest energy absorption bands in the
electronic spectra of the complexes in the visible region 450–480 nm are ascribed to MLCT
(metal to ligand charge transfer) transitions [30‒32].
5

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6
Figure 1. Electronic spectrum of [Ru(η ‒p‒cymene)(Cl)(L )].
4
‒6
1
The H NMR spectra of all the ligands and complexes were recorded in CDCl
the coordination mode of the Schiff base ligand to the ruthenium(II) ion. The Schiff base ligands
HL ‒HL ) shows a singlet in the δ 12.37‒14.29 ppm range can be attributed to the proton of the
OH group [33]. The azomethine proton (CH=N) was observed as a singlet at δ 8.73‒9.60 ppm
for the ligands HL to HL respectively. The multiplets of the aromatic protons of the ligands
3
to confirm
(
1
3
–
1
3
were in the region of δ 6.59–8.22 ppm. The pyrazole CH proton appears as a singlet in the range
.59–6.61 ppm. A sharp singlet at δ 3.88‒4.01 ppm in the spectra of ligand was attributed to
6
methyl and methoxy groups respectively. The singlet due to the –OH proton of the free ligand in
the region δ 12.37–14.29 ppm is absent in the complexes, 4‒6 supporting the coordination of the
phenolate oxygen to the Ru(II) ion. The imine proton (CH=N) of the complexes was observed as
a singlet in the region δ 8.52−8.81 ppm. In all the complexes, the four aromatic hydrogens of p-
cymene protons appear in the region of δ 3.98–5.40 ppm. Additionally, the methyl group of the
6

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p-cymene comes as a singlet around the region of δ 2.15–2.22 ppm. The isopropyl methyl
protons of the p‒cymene appeared as two sets of doublets in the region of δ 1.17–1.26 ppm.
Further, the isopropyl CH protons come in the region of δ 2.81–2.92 ppm as septet [34‒36]. The
1
13
representative H NMR and C NMR spectra of the ligands and complexes are shown in Figs.
S1‒S9 (supporting information).
2
.2 Crystal structure
Single crystal X‒ray diffraction analysis of the ligand and complex was performed to
confirm the structure of these complexes. The ORTEP view of ligand 2 and complex 6 is shown
in Figs. 2 & 3 and packing arrangement is given in Fig. 4. The summary of single crystal X‒ray
structure refinement is shown in Table 1 and selected bond parameters are listed in Table 2. The
complex crystallizes in the monoclinic space group C 2/c. The coordination geometry of the
ruthenium atoms is the classic three‐legged piano‐stool arrangement with a pseudo‒octahedral
geometry. The ruthenium centers have six-coordinate geometry assuming that the Schiff base
ligand, a chloro group and the centroid of the aromatic ring of the p‒cymene ring serve as a
three-coordinated ligand, which is common for half sandwich “piano-stool” structures [37−45].
The Schiff base ligand binds to ruthenium metal center via O, N atom forming six membered
ring bite angels of 86.28(11)° O(1)‒Ru(1)‒N(3), 85.00(10)° O(1)‒Ru(1)‒Cl(1), 86.06(9)° N(3)‒
Ru(1)‒Cl(1) and 120.5(4)° N(1)‒C(1)‒N(3). The Ru‒C distances are (2.157(4), 2.191(4),
2
.212(4), 2.204(3), 2.182(3) and 2.13–2.21 Å) typically found for p‒cymene coordinated
ruthenium centre [35, 36]. The bond distances around the ruthenium atom vary over a small
range Ru(1)‒O(1) 2.057(3) Å, Ru(1)‒N(3) 2.096(3) Å and N(1)‒N(3) 1.353(5) Å which was in
good agreement with other related p‒cymene ruthenium complexes containing [ON] anionic
bidentate ligands [46‒49].
7

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Figure 2. ORTEP diagram of the HL (2); ellipsoids are drawn at the 50% probability level.
2
8

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6
Figure 3. ORTEP diagram of the complex [Ru(η ‒p‒cymene)Cl(L )] (6); ellipsoids are drawn at
3
the 50% probability level.
9

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Figure 4. Packing diagram of complex 6.
1
0

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Table 1. Crystal data and structure refinement for ligand HL
2
and complex 6.
HL2
6
Empirical formula
Formula weight
Temperature
C H N O
307.35
296(2) K
C H Cl N O Ru
2
1279.12
296(2) K
18
17
3
2
63 62
4
6
2
Wavelength
Crystal system
Space group
0.71073 Å
Orthorhombic
P 212121
0.71073 Å
Monoclinic
C 2/c
Unit cell dimensions
a = 6.3165(4) Å
b = 8.4803(5) Å
c = 29.1434(17) Å
α= 90°.
β= 90°.
γ = 90°.
a = 26.3384(10) Å
b = 12.8242(5) Å
c = 17.4790(6) Å
α= 90°.
β= 103.131(2)°.
γ = 90°.
3
3
Volume
Z
1561.09(16) Å
4
5749.5(4) Å
4
3
3
Density (calculated)
1.308 Mg/m
1.478 Mg/m
-1
-1
Absorption coefficient
F(000)
0.087 mm
648
0.761 mm
2616
3
3
Crystal size
Theta range for data collection
Index ranges
0.22 x 0.14 x 0.08 mm
1.397 to 29.016°
0.350 x 0.300 x 0.220 mm
2.887 to 29.274°
-8<=h<=8, -11<=k<=11, -39<=l<=39
-36<=h<=35, -16<=k<=17, -23<=l<=23
Reflections collected
Independent reflections
Completeness to theta = 25.242°
9225
27948
7667 [R(int) = 0.0514]
99.3 %
4175 [R(int) = 0.0210]
99.4 %
2
2
Refinement method
Data / restraints / parameters
Full-matrix least-squares on F
3945 / 0 / 208
Full-matrix least-squares on F
7667 / 0 / 353
2
Goodness-of-fit on F
1.076
1.073
Final R indices [I>2sigma(I)]
R indices (all data)
Extinction coefficient
R
R
n/a
1
= 0.0463, wR
= 0.0596, wR
2
= 0.1170
= 0.1325
R
R
1
= 0.0546, wR
= 0.0902, wR
0.0022(2)
0.615 and -0.706 e.Å
2
= 0.1295
= 0.1464
1
2
1
2
-
3
-3
Largest diff. peak and hole
0.213 and -0.220 e.Å
1
1

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Table 2. Selected bond angle (˚) and length (Å) for Ligand HL
2
and complex 6.
HL2
6
Bond angle (˚)
N(1)‒N(2)‒C(10)
N(1)‒N(2)‒C(9)
N(2)‒N(1)‒C(7)
N(1)‒C(7)‒C(6)
O(1)‒C(17)‒C(12)
N(3)‒C(11)‒C(12)
119.9(2)
111.9(2)
105.0(2)
120.3(2)
122.9(2)
122.7(2)
N(2)‒C(1)‒N(3)
N(1)‒C(3)‒C(2)
N(1)‒C(3)‒C(4)
O(1)‒Ru(1)‒C(25)
N(3)‒Ru(1)‒Cl(1)
O(1)‒Ru(1)‒N(3)
O(1)‒Ru(1)‒Cl(1)
120.5(4)
120.4(4)
120.4(4)
109.32(14)
86.06(9)
86.28(11)
85.00(10)
Bond Length (Å)
N(1)‒C(7)
N(2)‒N(1)
N(3)‒C(9)
N(3)‒C(11)
C(17)‒O(1)
C(16)‒O(2)
1.341(3)
1.347(3)
Ru(1)‒Cl(1)
Ru(1)‒O(1)
Ru(1)‒N(3)
N(1)‒N(2)
C(13)‒O(1)
C(10)‒N(2)
C(1)‒N(2)
C(1)‒N(3)
2.430(11)
2.057(5)
2.096(3)
1.353(5)
1.293(4)
1.448(6)
1.359(5)
1.421(4)
1.388(3)
1.285(3)
1.345(3)
1.368(3)
1
2

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2
.3 Catalytic transfer hydrogenation of ketones
To evaluate the usefulness of synthesized
p
-cymene ruthenium(II) Schiff base
complexes, we investigated the catalytic application of the complex catalyst 4‒6 to the transfer
hydrogenation of various ketones. The catalytic reactions were performed using (5.0 mmol) of
benzophenone as model substrate, 0.2 mol% of complexes 4‒6 and KOH (0.03 mmol) in
2
‒propanol were refluxed for 3 h. All the complexes were found to be effective catalysts
affording conversions 80%, 84% and 95% respectively and the results are summarized in Table
3
.
a
Table 3. Catalytic activity of the complexes 4‒6 .
O
OH
Complex
catalyst (4-6)
i-PrOH/KOH/3h
_
_
__________________________________________________
b
Entry
Complex
Conversion (%)
__________________________________________________
1
2
3
4
5
6
80
84
95
_
__________________________________________________
a
o
Reaction conditions: reactions were carried out at 80 C using benzophenone (5.0 mmol),
catalyst (0.01 mmol), base (0.03 mmol) and
i
‒PrOH (5 mL).
b
Conversion was monitored by GC analysis and are average of two runs.
1
3

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2
.4 Effect of catalyst/substrate ratio and base variation study
The catalyst 6 was chosen for the subsequent reaction because it showed the highest
conversion. In order to optimize the reaction conditions, different catalyst and substrate ratios
were tested and the results are summarized in Table 4. Benzophenone was selected as a test-
substrate and allowed it to react in 2‒propanol with catalytic quantities of complex 6 in the
presence of KOH. The reaction proceeds with high yield of benzophenone to benzhydrol when a
C: S ratio of 1:500 (0.2 mol %) is used. When increasing the C/S ratios to 1:1000, 1:1500, and
1
:2000, the reaction proceeds with lower conversion. Thus, it was concluded that catalyst and
substrate ratio of 1:500 is the best compromise between optimal reaction rates in 2‒propanol.
Further, in order to improve the reaction conditions such as base and reaction
temperature, the transfer hydrogenation reaction was carried out the reaction using
benzophenone as substrate and complex 6 as a test catalyst in the presence of 2‒propanol with
various bases. The reaction rates were found to be strongly dependent on the base employed and
a variety of base was screened. A remarkable increase in the product formation was observed in
presence of strong inorganic bases like KOH or NaOH which gives higher conversions of 95%
2 3 2 3
and 89%, respectively. Whereas weak inorganic bases such as Na CO and K CO gives
moderate conversions of 60% and 58%, respectively. For organic bases such as Et N and
3
pyridine we observed only trace amounts of alcohol were formed. The conversions are
summarized in Table 4. Therefore, the activity trend is found to be in the order KOH > NaOH >
Na CO > K CO > Et N > pyridine, consistent with the relative strength of the bases.
2
3
2
3
3
1
4

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6
a
Table 4. Effect of catalyst/substrate ratio and base by [Ru(η ‒
p
3
‒cymene)(Cl)(L )] 6 .
O
OH
Complex (6)
(
0.2 mol%)
i-PrOH/KOH/3h
_
_
________________________________________________________________________
b
Entry
C/S ratio
Base
Time (h)
Conversion (%)
________________________________________________________________________
1
2
3
4
5
6
7
8
9
1
1
1:500
1:1000
1:1500
1:2000
1:500
500
KOH
KOH
KOH
KOH
-
3
3
3
3
95
82
76
60
0
3
c
KOH
NaOH
3
3
0
1:500
1:500
1:500
1:500
1:500
89
Na CO
10
10
12
12
60
2
3
K CO
2
58
3
0
1
Et N
Trace
3
Pyridine
Trace
_
_______________________________________________________________________
Reaction conditions: reactions were carried out at 80 C using benzophenone (5.0 mmol),
a
o
catalyst (0.01 mmol), base (0.03 mmol),
i
-PrOH (5 mL).
Conversion was monitored by GC analysis and are average of two runs.
Reaction carried out in the absence of catalyst.
b
c
6
a
Table 5. Transfer hydrogenation of ketones using Ru(η ‒p‒cymene)(Cl)(L )] 6 .
3
Complex (6)
0.2 mol%
OH
O
i-PrOH, KOH, 3h R1
R1
R2
R2
b
c
Entry
Substrates
Products
Conv. (%) TON
1
5

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O H
1
99
4 95
O
O H
2
9
5
47 5
41 5
O H
O
8
3
3
HC
3
HC
3
O H
O
8
0
4 00
4 65
4
H3CO
H3CO
C l
O H
O
93
5
6
C l
O H
O
96
4 80
Br
Br
O
O H
7
98
4
90
O2
N
O2 N
O
O
O H
8
9
9
2
4 60
47 0
O H
94
O
O H
1
0
92
4
4
60
90
O
O
O H
O H
O H
1
1
98
4
4
95
65
1
1
2
3
99
93
O
1
6

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a
o
Conditions: reactions were carried out at 80 C using 5.0 mmol of ketone, 0.01 mmol catalyst,
0
.03 mmol base in 5 mL i‒PrOH.
Catalyst/substrate/KOH ratio is 1:500:3.
b
Conversion was determined by GC analysis with authentic samples.
c
TON = ratio of moles of product formed to moles of catalyst used.
2
.5 Transfer hydrogenation of ketones
The catalytic transfer hydrogenation of ketones to alcohols in the presence of half
sandwich ruthenium(II) Schiff base complexes has been studied in isopropanol and KOH as a
base. Several aromatic, cyclic and aliphatic ketones were carried out with complex 6 and
the results are summarized in Table 5. The complex catalyzes transfer hydrogenation of
acetophenone with substituents of varying electronic properties were efficiently reduced to the
corresponding secondary alcohols with good to excellent conversions in all the cases over a
period of 3 h. The catalytic reduction of acetophenone into 1‒phenyl ethanol is obtained about
9
9%. Sterically hindered ketones such as benzophenone to their corresponding secondary alcohol
had good conversion about 95%. The electron donating substituent present in the substrates
observed to have slightly less activity in the reduction of ketones. In case of 4‒methyl
acetophenone and 4‒methoxy acetophenone (entries 3 and 4) conversions to their corresponding
alcohols are 83% and 80% respectively. The electron withdrawing substituent present in the
substrates found to play a significant role in the conversion of ketone to alcohols. Substrate with
electron withdrawing substituents such as Cl, Br and NO (entries 5, 6 and 7) gave excellent
2
conversions of 93%, 96% and 98% respectively. Cyclic ketones containing five six membered
rings (entries 8 and 9) were reduced effectively to give the corresponding alcohols with
conversions of up to 92% and 94%. The complex catalyst also efficiently catalyzed the reduction
of aliphatic ketones such as 2‒butanone, 2‒pentanone, diethyl ketone and 4‒methylpentan‒2‒
1
7

ACCEPTED MANUSCRIPT
one (entries 10 to 13) to their corresponding secondary alcohols having 92%, 98%, 99% and
9
3% respectively. Acetone was identified as the only by‒product in all the cases.
It is worth to note that the observed results are significantly better than those previously
reported [50‒52]. The advantage of the present catalytic system is the use of low catalyst loading
and less time. Further, the enhancement of the catalytic activity of the present complexes is may
be due to the unsymmetrical environment around the metal centre by the steric and electronic
nature of bidentate Schiff base ligands. In addition, the ease by which these catalysts are
prepared offers another important advantage. The work up process is very simple for this
catalytic system, as the catalyst is stable in all organic solvents. Though the mechanistic aspect
of the reaction was not studied, it is believed that the transfer hydrogenation proceeded through
Ru‒H intermediate, which was already proved by several research groups [53]. The formation of
Ru‒iso‒propoxide species which undergoes β-hydride elimination leads to form ruthenium metal
hydride species with the release of acetone. Insertion of ketone to Ru‒H species, resulting in the
secondary alkoxide which involves alcohol metathesis to give the alcoholic product and
regenerate the original catalyst.
3
. Conclusion
6
In summary, new air stable half-sandwich (η ‒p‒cymene) ruthenium(II) Schiff base
6
complexes of the type [Ru(η ‒
p
‒cymene)(Cl)(L )] with O, N chelating ligands have been
1‒3
synthesized. The characterization of all the complexes accomplished by analytical and spectral
1
13
(
FT‒IR, UV‒Vis, H NMR and C NMR) methods. The molecular structure of one of the
complex 6 was confirmed by the single crystal X‒ray diffraction method which reveals Schiff
base ligand coordinate to ruthenium via O, N donor and indicates the presence of pseudo
octahedral geometry. The catalytic efficiency of one of the complexes 6 were developed in
‐
1
8

ACCEPTED MANUSCRIPT
transfer hydrogenation reaction and was found to be an excellent catalyst among the series in the
conversion of ketones to alcohols with maximum conversion of 99%.
4
. Experimental section
4
.1 Reagents and materials
3 2
Commercial RuCl .3H O was purchased from Himedia Pvt. Ltd. The solvents were
purified and dried according to standard procedures [54]. 5‒amino‒1‒methyl‒3‒phenyl
pyrazole, salicylaldehyde, 2‒hydroxy‒3‒methoxy benzaldehyde and 2‒hydroxy‒1‒
naphthaldehyde were obtained from Aldrich. The starting precursor complex
6
[
(η ‒p‒cymene)Ru(µ‒Cl)Cl] [55] was prepared according to the reported procedure.
2
4
.2 Physical measurements
Microanalytical (C, H, N) data were obtained with a Vario EL III Elemental analyzer at
SAIF–Cochin. Melting Points were recorded in the Boetius micro heating table and are
uncorrected. The FT–IR spectra of the compounds were recorded in Agilent Resolution pro
‒
1
system spectrometer over the range 4000 to 400 cm . Electronic spectra of the complexes were
recorded in CHCl solution in a Cary 300 Bio UV–Vis Varian spectrophotometer in the range
3
1
13
8
00‒200 nm. The H NMR and C NMR spectra were recorded in CDCl with Bruker 300MHz
3
instrument using TMS as internal reference.
4
1 3
.3 Preparation of Schiff base ligands (HL ‒L ) (1‒3)
A methonalic solution of salicylaldehyde (or) 3‒methoxy salicylaldehyde (or) 2‒hydroxy
1‒naphtylaldehyde (0.122‒0.172g, 1 mmol) and 5‒amino‒1‒methyl‒3‒phenyl pyrazole
‒
(0.173g, 1 mmol) in 20 mL of methanol was stirred at room temperature for a 3 h. The yellow
1
9

ACCEPTED MANUSCRIPT
solids were filtered, washed with cooled methanol, dried in air, which was recrystallized from
warm methanol.
o
‒1
Spectral data for ligands. HL (1): Yield: 75 %. M. pt. 150 C. FT‒IR (cm ): 3320
1
1
ν(OH), 1620 ν(C=N),1280 ν(C‒O). H NMR (300 MHz, CDCl ): 12.37 (s, 1H, OH), 8.73
3
(
s, HC=N), 3.98 (s, 3H, CH ), 6.59 (s, 1H, CH) 6.96‒7.82 (m, Ar‒H).
3
o
‒1
HL (2): Yield: 82 %. M. pt. 180 C. FT‒IR (cm ): 3350 ν(OH), 1612 ν(C=N), 1296
2
1
ν(C‒O). H NMR (300 MHz, CDCl
3
): 12.81 (s, 1H, OH), 8.74 (s, HC=N), 3.97 (s, 3H, CH
3
),
3
.96 (s, 3H, OCH
3
), 6.61 (s, 1H, CH) 6.91‒7.82 (m, Ar‒H).
o
‒1
3
HL (3): Yield: 90 %. M. pt. 195 C. FT‒IR (cm ): 3399 ν(OH), 1618 ν(C=N), 1270
1
ν(C‒O). H NMR (300 MHz, CDCl ): 14.29 (s, 1H, OH), 9.60 (s, HC=N), 4.00 (s, 3H, CH ),
3
3
6
.66 (s, 1H, CH) 7.20‒8.22 (m, Ar‒H).
6
4
.4 Synthesis of (η ‒p‒cymene) ruthenium(II) Schiff base complexes (4‒6)
6
A mixture containing starting precursor [(η ‒
p‒cymene)Ru(µ‒Cl)Cl]2 (0.0918 g;
0
.15 mmol), Schiff base ligands (0.088‒0.098 g; 0.30 mmol), triethylamine (0.3 mL) in
dichloromethane (30 mL) was taken in a clean 100 ml round bottom flask and the reaction
mixture was stirred for 12 h at room temperature. The progress of the reaction was monitored
using TLC. At the end of the reaction, the solution was concentrated to about 3 mL and hexane
was added to initiate the precipitate of orange powder then it was filtered and washed with
hexane, and purified using column chromatography.
6
4
.4.1 [Ru(η ‒p‒cymene)(Cl)(L )] (4)
1
o
28 3
Red-brown solid. Yield: 60%. M. pt. 180 C. Anal. Calcd for C27H N ClORu: C, 59.28;
‒
1
H, 5.12; N, 7.68. Found: C, 59.18; H, 5.02; N, 7.56. FT‒IR cm ): 1605 ν(CH=N), 1328 ν(C‒O).
1
UV–Vis
λ
max (nm): 480, 375, 330. H NMR (300 MHz, CDCl
3
): δ (ppm) = 6.0–7.8 (m, Ar‒H),
2
0

ACCEPTED MANUSCRIPT
8
.6 (s, HC=N), 4.1 (s, CH
3
) 3.8 (d, 1H, cymene Ar
‒
H), 4.4 (d 1H, cymene Ar
‒
H), 5.1 (d 1H,
1
cymene Ar
‒
H), 5.4 (d 1H, cymene Ar
‒
H), 2.8 (m, H, CH of
p
‒
cymene), 2.2 (s, 3H, CH of p‒
3
1
3
cymene), 1.2 (dd, 6H, 2CH of p‒cymene). C NMR (100 MHz, CDCl , δ, ppm): 18.3 (CH of
3
3
3
p‒cymene), 21.5, 22.8 (2CH of p‒cymene), 37.0 (CH of ligand), 30.4 (CH of
p
‒
cymene), 82.3–
3
3
8
1
1
6.4 (aromatic carbons of p‒cymene), 97.5 and 102.0 (quaternary carbons of p‒cymene), 96.3,
55.4, 167.1 (pyrazole CHarom and Carom), 116.6, 117.7, 120.3, 122.9, 125.3, 127.5, 128.2, 129.4,
32.8, 135.8, 136.8 (CHarom and Carom), 149.9 (C═N), 167.2 (C─O).
6
4
.4.2 [Ru(η ‒p‒cymene)(Cl)(L )] (5)
2
o
Orange solid. Yield: 65%. M. pt. 195 C. Anal. Calcd for C H N ClO Ru: C, 58.28; H,
2
8
30
3
2
‒
1
5
.20; N, 7.28. Found: C, 58.15; H, 5.10; N, 7.12. FT‒IR cm ): 1600 ν(CH=N), 1331 ν(C‒O).
1
UV–Vis λmax (nm): 450, 380, 320. H NMR (300 MHz, CDCl ): δ (ppm) = 6.4–7.8 (m, Ar-H),
3
8
.7 (s, HC=N), 3.8 (s, OCH
3
), 4.0 (s, CH
3
), 4.1 (d, 1H, cymene Ar‒H), 4.4 (d 1H, cymene Ar‒
1
H), 5.3 (d 1H, cymene Ar
‒
H), 5.4 (d 1H, cymene Ar
‒
H), 2.9 (m, H, CH of
p
‒cymene), 2.1 (s,
1
3
3
1
H, CH of p‒cymene), 1.2 (dd, 6H, 2CH of p‒cymene). C NMR (100 MHz, CDCl , δ, ppm):
3 3 3
8.2 (CH of p‒cymene), 21.5, 22.8 (2CH of p‒cymene), 37.0 (CH of ligand), 30.3 (CH of p‒
3
3
3
cymene), 80.8–86.1 (aromatic carbons of p‒cymene), 97.4 and 102.4 (quaternary carbons of p‒
cymene), 96.3, 152.5, 159.1 (pyrazole CHarom and Carom), 113.8, 116.0, 117.6, 119.2, 125.3,
1
27.1, 128.1, 132.9 (CHarom and Carom), 149.9 (C═N), 166.9 (C─O).
6
4
.4.3 [Ru(η ‒p‒cymene)(Cl)(L )] (6)
3
o
Orange solid. Yield: 80%. M. pt. 210 C. Anal. Calcd for C H N ClORu: C, 62.36; H,
3
1
30
3
‒
1
5
.02; N, 7.04. Found: C, 62.08; H, 4.92; N, 6.90. FT‒IR cm ): 1602 ν(CH=N), 1320 ν(C‒O).
1
UV–Vis λmax (nm): 460, 365, 335. H NMR (300 MHz, CDCl ): δ (ppm) = 6.4–7.9 (m, Ar‒H),
3
8
3
.5 (s, HC=N), 4.1 (s, CH ), 4.4 (d, 1H, cymene Ar‒H), 5.2 (d 1H, cymene Ar‒H), 5.0 (d 1H,
2
1

ACCEPTED MANUSCRIPT
1
cymene Ar
‒
H), 5.4 (d 1H, cymene Ar
‒
H), 2.8 (m, H, CH of
p
‒
cymene), 2.2 (s, 3H, CH
3
of p‒
1
3
cymene), 1.2 (dd, 6H, 2CH of p‒cymene). C NMR (100 MHz, CDCl , δ, ppm): 18.4 (CH of
3
3
3
p‒cymene), 21.3, 22.9 (2CH of p‒cymene), 37.0 (CH of ligand), 30.5 (CH of
p
‒
cymene), 81.9–
3
3
8
1
1
6.6 (aromatic carbons of p‒cymene), 97.6 and 101.8 (quaternary carbons of p‒cymene), 96.3,
56.6, 159.6 (pyrazole CHarom and Carom), 119.0, 122.6, 125.1, 126.7, 127.9, 128.9, 133.0, 134.6,
37.4 (CHarom and Carom), 149.9 (C═N), 168.4 (C─O).
4
.5 X‒ray crystallography
Single crystals of ligand HL (2) and complex [(η ‒
6
p
‒cymene)ClRu(L )] (6) was grown
3
2
by slow evaporation of the solvent from solution of the respective complex in dichloromethane/
n-hexane mixture at room temperature. The data collection was carried out using a Bruker AXS
Kappa APEX II single crystal X‒ray diffractometer using monochromated Mo–Kα radiation
(kI = 0.71073 Å). Data was collected at 296 (2) K. The absorption corrections were performed
by the multi-scan method using SADABS software [56]. Corrections were made for Lorentz and
polarization effects. The structures were solved by direct methods (SHELXS 97) and refined by
full‒matrix least squares on F2 using SHELXL 97 [57]. All non‒hydrogen atoms were refined
anisotropically and the hydrogen atoms in these structures were located from the difference
Fourier map and constrained to the ideal positions in the refinement procedure. The unit cell
parameters were determined by the method of difference vectors using reflections scanned from
three different zones of the reciprocal lattice. Frame integration and data reduction were
performed using the Bruker SAINT‒Plus (Version 7.06a) software [58].
4
.6 Typical procedure for the catalytic transfer hydrogenation of ketones
In a dry round bottom flask under an atmosphere of nitrogen were placed an appropriate
amount of catalyst 4‒6 (0.01 mmol), (0.03 mmol) of KOH and (5.0 mmol) of ketones in
2
2

ACCEPTED MANUSCRIPT
2
‒propanol (5 mL) was added and the resulting mixture was refluxed for 3 h. After completion
of the reaction, the solvent was removed under reduced pressure. The catalyst was removed by
the addition of 15 mL of petroleum ether followed by filtration and subsequent neutralization
with dilute HCl. The combined organic fractions were dried with anhydrous Na SO . Percentage
2
4
of conversion was determined by GC analysis of the crude mixture and compared with the
authentic samples.
Acknowledgments
The authors express sincere thanks to Single Crystal X‒ray Diffraction Facility, SAIF
Gauhati University, for providing X‒ray data collection.
Appendix A. Supplementary material
1
13
H NMR and C NMR spectra for all the ligands and complexes are associated with this
article. Crystallographic data for the structural analysis have been deposited with Cambridge
crystallographic center, CCDC No. 1862859, 1850265. This can be obtained free of charge at
www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data
Center, 12, Union Road, Cambridge CB2 1EZ, UK; fax: (internet.) +44- 1223/336-033; E-mail:
deposit@ccdc.cam.ac.uk).
References
[
1] (a) S. -I. Murahashi (Ed.), Ruthenium in Organic Synthesis, Wiley-VCH, Weinheim (2004);
b) J. M. Stubbs, R. J. Hazlehurst, P. D. Boyle, J. M. Blacquiere, Organometallics 36 (2017)
692–1698; (c) M. Simonetti, G. J. P. Perry, X. C. Cambeiro, F. Julia´-Hernandez, J. N.
Arokianathar, I. Larrosa, J. Am. Chem. Soc. 138 (2016) 3596–3606; (d) J. Canivet, G. Süss-
Fink, Green Chem. 9 (2007) 391–397; (e) D. Sterk, M. Stephan, B. Mohar, Org. Lett.
2006) 5935–5938; (f) A. B. Chaplin, P. J. Dyson, Organometallics 26 (2007) 4357–4360.
(
1
8
(
2
3

ACCEPTED MANUSCRIPT
[
2] (a) C. S. Hauser, C. Slugovc, K. Mereiter, R. Schmid, K. Kirchner, L. Xiao, W.
Weissenteiner, J. Chem. Soc. Dalton Trans. (2001) 2989‒2995;(b) D. Zell, S. Warratz, D.
Gelman, S. J. Garden, L. Ackermann, Chem. Eur. J. 22 (2016) 1248–1252; (c) J. Malineni,
H. Keul, M. Moller, Dalton Trans. 44 (2015) 17409–17414.
[3] (a) H. Y. Rhyoo, H.‐J. Park, Y. K. Chung, J. Chem. Soc., Chem. Commun. (2001) 2064; (b)
F. Sepulveda, M. C. Carrion, A. D. Phillips, F. A. Jalon, P. J. Dyson, B. R. Manzano, Eur. J.
Inorg. Chem. (2017) 630–638. (c) K. M. Steward, E. C. Gentry, J. S. Johnson, J. Am. Chem.
Soc.134 (2012) 7329–7332; (d) P. Kacer, M. Kuzma, E. Leitmannova, L. Cerveny
Organomet. Compd. (2010) 373–401.
4] (a) M. J. Chow, C. Licona, Y. Qiang, D. Wong, G. Pastorin, C. Gaiddon, W. H. J. Ang,
,
[
J. Med. Chem. 57 (2014) 6043−6059; (b) K. N. Kumar, G. Venkatachalam, R. Ramesh, Y.
Liu, Polyhedron 27 (2008) 157–166.
[
5] (a) D. Tyagi, C. Binnani, R. K. Rai, A. D. Dwivedi, K. Gupta, P. –Z. Li, Y. Zhao, S. K. Singh
Inorg. Chem. 55 (2016) 6332–6343; (b) W. –G. Jia, H. Zhang, T. Zhang, S. Ling, Inorg.
Chem. Commun. 66 (2016) 15–18.
[6] J. M. Gichumbi, H. B. Friedrich B. Omondi, Inorg. Chimi. Acta. 456 (2017) 55‒63.
[7] G. Balamurugan, R. Ramesh, J. G. Malecki, ChemistrySelect 2 (2017) 10603–10608.
[8] S. Muthumari, R. Ramesh, ChemistrySelect 3 (2018) 3036–3041.
[9] T. S. Manikandan, R. Ramesh, N. Shivalingegowda, L. N. Krishnappagowda
ChemistrySelect 3 (2018) 1561–1568.
[10] S. Saranya, R. Ramesh, J. G. Małecki, Eur. J. Org. Chem. (2017) 6726–6733.
[
11] M. Ramesh, M. D. Kumar, M. Jaccob, B. Therrien, G. Venkatachalam, Inorg. Chimi. Acta
77 (2018) 40–50.
12] (a) S. Dayan, N. Kayaci, N. O. Kalaycioglu, O. Dayan, E. C. Ozturk, Inorg. Chimi. Acta
.
4
[
.
2
4

ACCEPTED MANUSCRIPT
401 (2013) 107–113; (b) S. Dayan N. K. Ozpozan, N. Özdemir, O. Dayan J. Organomet.
Chem. 770 (2014) 21‒28; (c) J. M. Gichumbi, H. B. Friedrich, B. Omondi, J. Organomet.
Chem. 808 (2016) 87‒96.
[
13] (a) M. Ramesh G. Venkatachalam, ChemistrySelect 3 (2018) 9056–9061; (b) A.
Kanchanadevi, R. Ramesh, D. Semeril, Inorg. Chem. Commun. 56 (2015) 116–119; (c) N.
Raja, B. Therrien, J. Organomet. Chem. 765 (2014) 1–7; (d) M. Ramesh, M. Kalidass, M.
Jaccob, D. Kaleeswaran, G. Venkatachalam, J. Organomet. Chem. 830 (2017) 33–41.
14] A. D. Dwivedi, C. Binnani, D. Tyagi, K. S. Rawat, P. –Z. Li, Y. Zhao, S. M. Mobin, B.
Pathak, S. K. Singh, Inorg. Chem. 55 (2016) 6739–6749.
[
[
15] (a) M. C. Carrion, M. Ruiz-Castaneda, G. Espino, C. Aliende, L. Santos, A. M. Rodriguez,
B. R. Manzano, F. A. Jalon, A. Lledos, ACS Catal. 4 (2014) 1040–1053; (b) M. M. Sheeba,
M. M. Tamizh, M. L. J. Farrugia, A. Endo, R. Karvembu, Organometallics 33 (2014)
5
40−550; (c) O. Prakash, H. Joshi, K. N. Sharma, P. L. Gupta, A. K. Singh,
Organometallics 33 (2014) 3804−3812; (d) C. Romain, S. Gaillard, M. K. Elmkaddem, L.
Toupet, C. Fischmeister, C. M. Thomas, J. –L. Renaud, Organometallics 29 (2010)
1
992−1995; (e) M. C. Carrión, F. Sepúlveda, F. A. Jalón, B. R. Manzano, A. M.
Rodríguez, Organometallics 28 (2009) 3822−3833; (f) Z. Fang, M. Wills, J. Org. Chem. 78
2013) 8594−8605; g) A. M. Hayes, D. J. Morris, G. J. Clarkson, M. Wills, J. Am. Chem.
(
Soc. 127 (2005) 7318−7319.
[
16] (a) K. Y. Ghebreyessus, J. H. Nelson, J. Organomet. Chem. 669 (2003) 48‒56; (b) T.
Ikariya, A. J. Blacker, Acc. Chem. Res. 40 (2007) 1300‒1308; (c) L. Taghizadeh
Ghoochany, S. Farsadpour, Y. Sun, W. R. Thiel, Eur. J. Inorg. Chem. (2011) 3431–3437.
17]. a) R. Noyori, M. Yamakawa, S. Hashiguchi, J. Org. Chem. 66 (2001) 7931−7944;
b) M. Yamakawa, H. Ito, R. Noyori, R. J. Am. Chem. Soc. 122 (2000) 1466−1478.
[
2
5

ACCEPTED MANUSCRIPT
[18]. B. Paul, K. Chakrabarti, S. Kundu, Dalton. Trans. 45 (2016) 11162-11171.
[19]. N. Mohan, S, Muthumari, R. Ramesh, Appl. Organomet. Chem.31 (2017) 3648−3656.
[20] (a) W. Baratta, J. Schütz, E. Herdtweck, W. A. Herrmann, P. Rigo, J. Organomet. Chem
.
6
90 (2005) 5570‒5575; (b) W. Baratta, E. Herdtweck, K. Siega, M. Toniutti, P. Rigo,
Organometallics 24 (2005) 1660‒1669; (c) W. Baratta, M. Ballico, G. Esposito, P. Rigo,
Chem Eur. J. 14 (2008) 5588‒5595; (d) W. Baratta, K. Siega, P. Rigo, Adv. Synth. Catal
49 (2007) 1633‒1636.
21] (a) M. Ramesh, G. Prabusankar, G. Venkatachalam, Inorg. Chem. Commun. 79 (2017) 89–
4; (b) N. Raja, M.U. Raja, R. Ramesh, Inorg. Chem. Commun. 19 (2012) 51‒54.
22] (a) J. M. Gichumbi, H. B. Friedrich, B. Omondi, J. Mol. Catal. A: Chem. 1416 (2016) 29–
8; (b) G.Venkatachalam, R. Ramesh, Inorg. Chem. Commun. 9 (2006) 703‒707.
.
.
3
[
[
[
9
3
23] P. Govindaswamy, J. Canivet, B. Therrien, G. Suss-Fink, P. Stepnika, J. Ludvık,
J. Organomet. Chem. 692 (2007) 3664–3675.
[
24] E. Peker, S. Serin, Syn. React. Inorg. Met. 34 (2004) 859-872.
25] M. Ramesh, M. D. Kumar, M. Jaccob, D. Kaleeswaran, G. Venkatachalam, Inorg. Chem
Commun. 85 (2017) 26–31.
[
.
[
26] J. Dutta, M. G. Richmond, S. Bhattacharya, Eur. J. Inorg. Chem. 27 (2014) 4600.
27] R. M. Fuquen, F. Cuenú, J. E. Torres, G. D. Vega, E. Galarza, R. Abonia, A. R.
Kennedy, J. Mol. Struct. 1150 (2017) 366‒373.
[
[
[
[
[
[
28] G. N. Babu, A. R. B. Rao, S. Keesara, S. Pal, J. Organomet. Chem. 848 (2017) 243–248.
29] S. J. Pradeepa, N. Sundaraganesan, Spectrochimi. Acta A. 125 (2014) 211–221.
30] K. Ghosh, R. Kumar, K. Kumar, A. Ratnam, U. P. Singh, RSC Adv. 4 (2014) 43599–43605.
31] T. D. Thangadurai, K. Natarajan, Transit. Met. Chem. 25 (2000) 347–351.
32] A. B. P. Lever, Inorganic Electronic Spectroscopy, 2nd ed., Elsiever, New York (1984).
2
6

ACCEPTED MANUSCRIPT
[33] E. Ispir, Dyes Pigments. 82 (2009) 13‒19.
[
34] (a) A. F. A. Peacock, M. Melchart, R. J. Deeth, A. Habtemariam, S. Parsons, P. Sadler,
Chem. Eur. J. 13 (2007) 2601‒2613; (b) R. Fernandez, M. Melchart, A. Habtemariam, S.
Parsons, P. J. Sadler, Chem. Eur. J. 16 (2004) 5173‒5183.
[35] W. –G. Jia, H. Zhang, T. Zhang, D. Xie, S. Ling, E. –H. Sheng, Organometallics 35 (2015)
503-512.
[
36] R. Pettinari, C. Pettinari, F. Marchetti, C. M. Clavel, R. Scopelliti, P. J. Dyson,
Organometallics 32 (2013) 309−316.
[37] H. Li, Z. –J. Yao, D. Liu, G. –X. Jin, Coord. Chem. Rev. (2015) 293−294.
[38] Y. –F. Han, G. –X. Jin, Acc. Chem. Res. 47 (2014) 3571−3579.
[39] Y. –F. Han, G. –X. Jin, Chem. Soc. Rev. 43 (2014) 2799−2823.
[40] L. Zhang, Y. –J. Lin, Z. –H. Li, G. –X. Jin, J. Am. Chem. Soc. 137 (2015) 13670−13678.
[41] H. Li, Y. –F. Han, Y. –J. Lin, Z. –W. Guo, G. –X. Jin, J. Am. Chem. Soc. 136 (2014)
2982−2985.
[42] D. –H. Wu, C. Ji, Y. –Z. Li, H. Yan, Organometallics 26 (2007) 1560−1562.
[43] P. Kumar, R. K. Gupta, D. S. Pandey, Chem. Soc. Rev. 43 (2014) 707−733.
[44] A. Mishra, Y. J. Jeong, J. –H. Jo, S. C. Kang, H. Kim, K. –W. Chi, Organometallics
3
3 (2014) 1144−1151.
[
[
[
45] P. Crochet, V. Cadierno, Dalton Trans. 43 (2014) 12447−12462.
46] J. G. Malecki, Struct. Chem. 23 (2012) 461−472.
47] R. Pettinari, F. Marchetti, C. Pettinari, A. Petrini, R. Scopelliti, C. M. Clavel, P. Dyson,
J. Inorg. Chem. 53 (2014) 13105−13111.
[48] R. M. Lord, A. J. Hebden, C. M. Pask, I. R. Henderson, S. J. Allison, S. L. Shepherd,
R. M. Phillips, P. C. McGowan, J. Med. Chem. 58 (2015) 4940−4953.
2
7

ACCEPTED MANUSCRIPT
[
49] J. G. Malecki, R. Kruszynski, M. Jaworska, P. Lodowski, Z. Mazurak, J. Organomet.
Chem. 693 (2008) 1096−1108.
[50] M. C. Carrion, F. Sepulveda, F. A. Jalon, B. R. Manzano, Organometallics 28 (2009)
3822‒3833.
[
51] P. Kumar, M. Yadav, A. K. Singh, D. S. Pandey, Eur. J. Inorg. Chem. (2010) 704‒715.
52] I. Nieto, M. S. Livings, J. B. Sacci, L. E. Reuther, M. Zeller, E. T. Papish,
Organometallics 30 (2011) 6339‒6342.
[
[53] (a) B. Paul, K. Chakrabarti, S. Kundu, Dalton Trans. 45 (2016) 11162–11171; (b) K. Li, J.
–
L. Niu, M. -Z. Yang, Z. Li, L. -Y. Wu, X. -Q. Hao, M. -P. Song, Organometallics 34
(2015) 1170–1176. (c) W. Du, Q. Wang, L. Wang, Z. Yu, Organometallics 33 (2014)
9
1
74–982; (d) Q. Wang, W. Du, T. Liu, H. Chai, Z. Yu, Tetrahedron Lett. 55 (2014) 1585–
588; (e) W. Du, P. Wu, Q. Wang, Z. Yu, Organometallics 32 (2013) 3083–3090; (f) A.
Maity, A. Sil, S. K. Patra, Eur. J. Inorg. Chem. DOI: 10.1002/ejic.201800585; (g) J. E.
Backvall, J. Organomet. Chem. 652 (2002) 105‒111; (h) N. Menashe, Y. Shvo,
Organometallics 10 (1991) 3885‒3891; (i) T. Fuji, Y. Saito, J. Mol. Cat. 67 (1991) 185‒
1
90.
[54] D. D. Perrin, W. L. F. Armarego, Purification of Laboratory Chemicals, fourth ed.,
Butterworths-Heinemann, London, (1996).
[
55] M. A. Bennett, A. K. Smith, J. Chem. Soc. Dalton Trans. (1974) 233‒241.
56] F. H. Allen, W. D. S. Motherwell, P. R. Raithby, G. P. Shields, R. Taylor, New J.
Chem. 23 (1999) 25‒34.
[
[
57] G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr. 64 (2008) 112‒122.
58] Bruker-Nonius (2004) APEX-II and SAINT-Plus (Version 7.06a), Bruker AXS Inc.,
Madison, Wisconsin, USA.
[
2
8