Water soluble Ru (II)–p-cymene complexes of chiral aroylthiourea ligands derived from unprotected D/L-alanine as proficient catalysts for asymmetric transfer hydrogenation of ketones

Article abstract of DOI:10.1002/aoc.4667

The newfangled chiral aroylthiourea ligands (L1-L6) were produced from unprotected D/L-alanine and their water soluble Ru (II) organometallic catalysts (1–6) were designed from their reaction with [RuCl₂(η⁶-p-cymene)]₂. The analytical and spectral methods were used to confirm the structure of the ligands and complexes. The solid state structure of L1, 5 and 6 was confirmed by single crystal XRD. The organometallic compounds (1–6) catalyzed the asymmetric transfer hydrogenation of aromatic, heteroaromatic and bulky ketones to yield respective enantiopure secondary alcohols with admirable conversions (up to 99%) and attractive enantiomeric excesses (ee up to 98%), in presence of formic acid and triethylamine in water medium under non-inert atmospheric conditions.

Full text of DOI:10.1002/aoc.4667

Received: 12 August 2018
DOI: 10.1002/aoc.4667
Revised: 22 September 2018
Accepted: 25 September 2018
F U L L P A P E R
Water soluble Ru (II)–p‐cymene complexes of chiral
aroylthiourea ligands derived from unprotected D/L‐alanine
as proficient catalysts for asymmetric transfer
hydrogenation of ketones
Mani Mary Sheeba1 | Manoharan Muthu Tamizh2
Ramasamy Karvembu1
| Nattamai S.P. Bhuvanesh3 |
1 Department of Chemistry, National
The newfangled chiral aroylthiourea ligands (L1‐L6) were produced from
unprotected D/L‐alanine and their water soluble Ru (II) organometallic cata-
lysts (1–6) were designed from their reaction with [RuCl2(η6‐p‐cymene)]2.
The analytical and spectral methods were used to confirm the structure of
the ligands and complexes. The solid state structure of L1, 5 and 6 was con-
firmed by single crystal XRD. The organometallic compounds (1–6) catalyzed
the asymmetric transfer hydrogenation of aromatic, heteroaromatic and bulky
ketones to yield respective enantiopure secondary alcohols with admirable con-
versions (up to 99%) and attractive enantiomeric excesses (ee up to 98%), in
presence of formic acid and triethylamine in water medium under non‐inert
atmospheric conditions.
Institute of Technology, Tiruchirappalli
620 015, India
2 Department of Chemistry, Siddha
Central Research Institute, Central
Council for Research in Siddha,
Arumbakkam, Chennai 600 106, India
3 Department of Chemistry, Texas A & M
University, College Station, TX 77842, USA
Correspondence
Ramasamy Karvembu, Department of
Chemistry, National Institute of
Technology, Tiruchirappalli 620 015, India.
Email: kar@nitt.edu
Funding information
KEYWORDS
Department of Science and Technology,
Ministry of Science and Technology, Gov-
ernment of India, Grant/Award Number:
IF110522
aqueous medium, aroylthiourea asymmetric hydrogenation, ruthenium
1 | INTRODUCTION
metabolic enzymes, transporters, etc.).[6] Chiral alcohols
are one of the utmost essential key chiral building
Water is an eco‐friendly solvent in catalysis and also,
diverse interactions are possible among water, catalyst
and substrate, which make the catalytic system homoge-
neous and effective. The development of water soluble
chiral catalysts is a crucial area of green chemistry. Amino
acids or altered amino acids are applied as chiral catalysts
in water medium in the Diels‐Alder,[1] Michael,[2] asym-
metric transfer hydrogenation (of ketones[3,4] and
imines[4]) and direct asymmetric aldol reactions.[5]
blocks for various single enantiomer pharmaceuti-
cals.[7,8] Asymmetric reduction of pro‐chiral ketones is
a powerful method for the production of chiral alcohols.
Asymmetric transfer hydrogenation (ATH) of ketones by
organometallic homogeneous catalysis in water is of
abundant attention in green chemistry. Recently, many
have described the ATH of ketones in water solvent
under non‐inert conditions, which are useful for indus-
trial applications.[4,9–29] Chiral Ru (II)‐p‐cymene com-
plexes are found to be promising catalysts for ATH of
ketones. But there are only a few reports on Ru‐p‐
cymene complex‐catalyzed ATH of ketones to resultant
The isolation of pure chiral compounds is of signifi-
cance as each enantiomer can have different properties
in biological systems (asymmetric protein targets,
Appl Organometal Chem. 2018;e4667.
wileyonlinelibrary.com/journal/aoc
© 2018 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4667

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SHEEBA ET AL.
chiral alcohols in an aqueous medium. The chiral
ligands used in these systems are, (R)‐N‐(4‐fluorophenyl)-
on a Sigma melting point apparatus and are uncorrected.
GC–MS measurements for catalytic experiments were
performed using a Shimadzu GCMS‐QP 2010 Ultra gas
chromatograph mass spectrometer with a Restek‐5 capil-
lary column. For GC measurements, Shimadzu GC 2010
was used with the same column. Enantiomeric excesses
(ee) were determined using a Shimadzu HPLC instru-
ment with a Daicel Chiralcel OB‐H column. Specific
rotation values were measured on a Rudolph Autopol
IV polarimeter.
pyrrolidine‐2‐carboxamide,[13]
bis(2‐aminophenyl)ethyl)‐4‐methylbenzene
N‐((1S,2S)‐2‐amino‐1,2‐
sulfon-
amide,[4] sodium‐2,2′‐((1R,2R)‐1‐amino‐2‐(4‐methylphe-
nylsulfonamido)ethane‐1,2‐diyl)dibenzenesulfonate,[12]
N‐(p‐toluenesulfonyl)‐1,2‐diphenyl‐ethylenediamine,[11]
N‐((1S,2S)‐2‐aminocyclohexyl)‐4‐methyl benzenesulfo-
namide[30] and (−)‐ephedrine hydrochloride.[21]
In metal‐catalyzed reactions, the unprotected amino
acids are infrequently used as chiral‐influence.[31] The
aroylthiourea ligands derived from D/L‐alanine have
been utilized in the unprotected form in this work due
to the expectation that the carboxylic acid group might
promote the solubility of the complexes in water.[32] The
chiral half‐sandwich Ru (II)‐arene complexes catalyze
various asymmetric transformations.[33] Steric factors of
the arene complexes help to get high stereoselectivity
in organic synthesis.[33] Simple amino acids are complexed
with Ru‐p‐cymene dimer, where the ligands exhibit
bidentate (O, N) coordination mode.[34] The aroylthiourea
ligands obtained from amino acids may provide more
opportunity for tuning the electronic property of the metal.
Our earlier attempt to prepare water soluble Ru‐p‐cymene
complexes using D/L‐phenylalanine‐aroylthiourea ligands
did not succeed as amino acid was converted in to its
ester during the complexation.[35] Fortunately, amino acid
in D/L‐alanine derivative of aroylthiourea is unchanged
when it is reacted with [RuCl2(η6‐p‐cymene)]2. In this
article, the preparation and characterization of new chiral
water soluble Ru (II)‐p‐cymene complexes (1–6) bearing
enantiopure D/L‐alanine‐aroylthiourea ligands (L1‐L6)
are described. The organometallic compounds (1–6) are
utilized as active catalysts for the ATH of aromatic ketones
to result enantiopure alcohols in aqueous medium
employing formic acid and triethylamine as a hydrogen
source and base respectively.
2.2 | Synthesis of L1‐L6
A solution of benzoyl chloride (0.6 ml, 5 mmol)/thio-
phene‐2‐carbonyl chloride (0.5 ml, 5 mmol) /furan‐2‐
carbonyl chloride (0.5 ml, 5 mmol) in acetone (30 ml)
was added to a suspension of potassium thiocyanate
(0.4859 g, 5 mmol) in acetone (30 ml). The reaction mix-
ture was heated under reflux for 45 min and then cooled
to room temperature. A solution of D/L‐alanine (0.4454 g,
5 mmol) in acetone (40 ml) and ethanol (20 ml) was
added, and the resulting mixture was stirred for 15 hr at
27 °C. Hydrochloric acid (0.1 N, 300 ml) was then added,
and the resulting solid was filtered off. The solid product
was washed with water and purified by recrystallization
from ethanol/dichloromethane mixture (1/2).
2.2.1 | (R)‐2‐(3‐benzoylthioureido)
propanoic acid (L1)
Yield: 74%, 0.93 g. M.p.: 134 °C. [α]D27: +11°. Anal. calcd
for C11H12N2O3S: C, 52.37; H, 4.79; N, 11.10; S, 12.71.
Found: C, 52.11; H, 4.57; N, 10.98; S, 12.58. H NMR δ,
1
ppm (500 MHz, DMSO‐d6): 1.48 (d, 3H, J = 10 Hz,
CH3), 4.79 (m, 1H, C*HMe), 7.50–7.94 (m, 5H, CH of phe-
nyl rings), 11.30 (d, 1H, J = 5 Hz, C=S attached N‐H),
11.44 (s, 1H, C=O and C=S attached N‐H), 13.52 (bs,
1H, COOH). 13C NMR δ, ppm (125 MHz, DMSO‐d6):
17.2 (CH3), 53.3 (asymmetric C), 128.3, 128.4, 132.1,
132.9 (aromatic), 168.2 (C=O), 172.8 (C=S), 179.5
(COOH). FT‐IR (KBr, cm−1): 3385 (m, ν (amide N‐H)),
3153 (s, ν (thiourea N‐H)), 1729 (s, ν (COOH)), 1679 (s,
ν(C=O)), 1258 (s, ν(C=S)).
2 | EXPERIMENTAL
2.1 | Materials and instrumentation
[RuCl2(η6‐p‐cymene)]2 was synthesized by using a litera-
ture procedure.[36] UV–visible spectra were recorded
using a Shimadzu 2600 spectrophotometer, operating in
the range of 200–800 nm. FT‐IR spectra were recorded
in the range of 600–4000 cm−1 on a Nicolet iS5 FT‐IR
spectrophotometer as KBr pellets. CHNS analyses were
performed using a Perkin Elmer 2400 series II elemental
2.2.2 | (S)‐2‐(3‐benzoylthioureido)
propanoic acid (L2)
Yield: 72%, 0.91 g. M.p.: 135 °C. [α]D27: − 13°. Anal. calcd
for C11H12N2O3S: C, 52.37; H, 4.79; N, 11.10; S, 12.71.
Found: C, 52.13; H, 4.59; N, 11.01; S, 12.54. H NMR δ,
ppm (500 MHz, DMSO‐d6): 1.49 (d, 3H, J = 5 Hz, CH3),
1
analyzer. H and 13C NMR spectra were recorded on a
1
Bruker 500 MHz and 125 MHz spectrometer, respectively.
Melting points were determined in open capillary tubes

SHEEBA ET AL.
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4.85 (m, 1H, C*HMe), 7.48–7.95 (m, 5H, CH of phenyl
rings), 11.29 (d, 1H, J = 5 Hz, C=S attached N‐H), 11.49
(s, 1H, C=O and C=S attached N‐H), 13.15 (bs, 1H,
COOH). 13C NMR δ, ppm (125 MHz, DMSO‐d6): 17.1
(CH3), 53.0 (asymmetric C), 128.3, 128.5, 132.0, 133.0
(aromatic), 168.4 (C=O), 172.8 (C=S), 179.8 (COOH).
FT‐IR (KBr, cm−1): 3384 (m, ν (amide N‐H)), 3157 (s, ν
(thiourea N‐H)), 1728 (s, ν (COOH)), 1679 (s, ν(C=O)),
1258 (s, ν(C=S)).
4.82 (m, 1H, C*HMe), 6.73–8.05 (m, 3H, CH of furan
ring), 11.05 (d, 1H, J = 10 Hz, C=S attached N‐H),
11.23 (s, 1H, C=O and C=S attached N‐H), 13.17 (bs,
1H, COOH). 13C NMR δ, ppm (125 MHz, DMSO‐d6):
17.1 (CH3), 53.0 (asymmetric C), 112.5, 118.4, 144.5,
148.3 (aromatic), 157.7 (C=O), 172.7 (C=S), 179.4
(COOH). FT‐IR (KBr, cm−1): 3263 (m, ν (amide N‐H)),
3153 (s, ν (thiourea N‐H)), 1727 (s, ν (COOH)), 1674 (s,
ν(C=O)), 1283 (s, ν(C=S)).
2.2.3 | (R)‐2‐(3‐(thiophene‐2‐carbonyl)
thioureido) propanoic acid (L3)
2.2.6 | (S)‐2‐(3‐(furan‐2‐carbonyl)
thioureido) propanoic acid (L6)
Yield: 78%, 1.06 g. M.p.: 144 °C. [α]D27: +62°. Anal. calcd
Yield: 75%, 0.96 g. M.p.: 115 °C. [α]D27: − 18°. Anal. calcd
for C9H10N2O3S2: C, 41.85; H, 3.90; N, 10.84; S, 24.83.
Found: C, 41.73; H, 3.77; N, 10.78; S, 24.78. H NMR δ,
for C9H10N2O4S: C, 44.62; H, 4.16; N, 11.56; S, 13.24.
Found: C, 44.52; H, 4.05; N, 11.49; S, 13.15. H NMR δ,
1
1
ppm (500 MHz, DMSO‐d6): 1.40 (d, 3H, J = 5 Hz, CH3),
4.75 (m, 1H, C*HMe), 7.16–8.28 (m, 3H, CH of thiophene
ring), 11.49 (d, 1H, J = 5 Hz, C=S attached N‐H), 11.08 (s,
1H, C=O and C=S attached N‐H), 13.08 (bs, 1H, COOH).
13C NMR δ, ppm (125 MHz, DMSO‐d6): 17.6 (CH3), 53.5
(asymmetric C), 129.2, 133.0, 135.7, 137.0 (aromatic),
162.7 (C=O), 173.3 (C=S), 180.0 (COOH). FT‐IR (KBr,
cm−1): 3261 (m, ν (amide N‐H)), 3110 (s, ν (thiourea N‐
H)), 1717 (s, ν (COOH)), 1659 (s, ν(C=O)), 1271 (s,
ν(C=S)).
ppm (500 MHz, DMSO‐d6): 1.47 (d, 3H, J = 5 Hz, CH3),
4.82 (m, 1H, C*HMe), 6.73–8.05 (m, 3H, CH of furan
ring), 11.05 (d, 1H, J = 10 Hz, C=S attached N‐H),
11.23 (s, 1H, C=O and C=S attached N‐H), 13.20 (bs,
1H, COOH). 13C NMR δ, ppm (125 MHz, DMSO‐d6):
17.1 (CH3), 53.0 (asymmetric C), 112.5, 118.5, 144.5,
148.3 (aromatic), 157.8 (C=O), 172.8 (C=S), 179.5
(COOH). FT‐IR (KBr, cm−1): 3264 (m, ν (amide N‐H)),
3154 (s, ν (thiourea N‐H)), 1729 (s, ν (COOH)), 1675 (s,
ν(C=O)), 1284 (s, ν(C=S)).
2.3 | Synthesis of Ru (II)‐p‐cymene
complexes 1–6
2.2.4 | (S)‐2‐(3‐(thiophene‐2‐carbonyl)
thioureido) propanoic acid (L4)
Yield: 75%, 1.01 g. M.p.: 143 °C. [α]D27: − 58°. Anal. calcd
[RuCl2(η6‐p‐cymene)]2 (122.5 mg, 0.2 mmol) and (R)/
(S)‐2‐(3‐benzoylthioureido) propanoic acid (101 mg,
for C9H10N2O3S2: C, 41.85; H, 3.90; N, 10.84; S, 24.83.
1
Found: C, 41.72; H, 3.78; N, 10.69; S, 24.76. H NMR δ,
0.4
mmol)
or
(R)/(S)‐2‐(3‐(thiophene‐2‐carbonyl)
ppm (500 MHz, DMSO‐d6): 1.40 (d, 3H, J = 5 Hz, CH3),
4.75 (m, 1H, C*HMe), 7.16–8.29 (m, 3H, CH of thiophene
ring), 11.08 (d, 1H, J = 5 Hz, C=S attached N‐H), 11.49 (s,
1H, C=O and C=S attached N‐H), 13.11 (bs, 1H, COOH).
13C NMR δ, ppm (125 MHz, DMSO‐d6): 17.6 (CH3), 53.5
(asymmetric C), 129.1, 133.0, 135.7, 137.0 (aromatic),
162.7 (C=O), 173.3 (C=S), 180.0 (COOH). FT‐IR (KBr,
cm−1): 3254 (m, ν (amide N‐H)), 3106 (s, ν (thiourea N‐
H)), 1718 (s, ν (COOH)), 1659 (s, ν(C=O)), 1274 (s,
ν(C=S)).
thioureido) propanoic acid (103 mg, 0.4 mmol) or (R)/
(S)‐2‐(3‐(furan‐2‐carbonyl)thioureido) propanoic acid
(96.9 mg, 0.4 mmol) were dissolved in toluene (20 mL)
and stirred for 4 hr at 27 °C. During the reaction, an
orange precipitate was formed, further, the addition of
hexane gave an orange color solid product. The product
was collected by filtration, washed with hexane and dried
in vacuo.
2.3.1 | [RuCl2(η6‐p‐cymene)L1] (1)
Yield: 74%, 165 mg. M.p.: 167 °C. [α]D27: − 74°. Anal. calcd
2.2.5 | (R)‐2‐(3‐(furan‐2‐carbonyl)
for C21H26Cl2N2O3RuS: C, 45.16; H, 4.69; N, 5.02; S, 5.74.
thioureido) propanoic acid (L5)
1
Found: C, 45.02; H, 4.55; N, 4.89; S, 5.65. H NMR δ,
Yield: 76%, 0.98 g. M.p.: 114 °C. [α]D27: +16°. Anal. calcd
for C9H10N2O4S: C, 44.62; H, 4.16; N, 11.56; S, 13.24.
Found: C, 44.54; H, 4.07; N, 11.48; S, 13.18. H NMR δ,
ppm (500 MHz, DMSO‐d6): 1.47 (d, 3H, J = 5 Hz, CH3),
ppm (500 MHz, DMSO‐d6): 1.19 (d, 6H, J = 7.0 Hz, 2CH3
of p‐cymene), 1.49 (d, 3H, J = 7.2 Hz, CH3 of the ligand),
2.08 (s, 3H, CH3 of p‐cymene), 2.83 (m, 1H, CH of
p‐cymene), 4.85 (m, 1H, C*HMe), 5.76–5.81 (m, 4H,
1

4 of 12
SHEEBA ET AL.
aromatic protons of p‐cymene), 7.50–7.94 (m, 5H, aro-
matic protons of the ligand), 11.29 (d, J = 7.0 Hz, 1H,
C=S attached N‐H), 11.49 (s, 1H, C=O and C=S attached
N‐H), 13.22 (bs, 1H, COOH). 13C NMR δ, ppm (125 MHz,
DMSO‐d6): 17.1 (CH3 of the ligand), 17.8 (CH3 of
p‐cymene), 21.4 (2CH3 of p‐cymene), 29.9 (CH of
p‐cymene), 53.0 (asymmetric carbon), 85.4–86.3 (aromatic
carbons of p‐cymene), 100.0 and 106.3 (quaternary car-
bons of p‐cymene), 128.3, 128.5, 132.0, 133.0 (CH), 168.4
(C=O), 172.8 (C=S), 179.8 (COOH). FT‐IR (KBr, cm−1):
3217 (m, ν (amide N‐H)), 3150 (s, ν (thiourea N‐H)), 1672
(s, ν(C=O)), 1741 (s, ν (COOH)), 1193 (s, ν(C=S)). UV–
C=O and C=S attached N‐H), 13.20 (bs, 1H, COOH).
13C NMR δ, ppm (125 MHz, DMSO‐d6): 17.1 (CH3 of
the ligand), 17.8 (CH3 of p‐cymene), 21.4 (2CH3 of
p‐cymene), 29.9 (CH of p‐cymene), 53.0 (asymmetric car-
bon), 85.4–86.3 (aromatic carbons of p‐cymene), 100.0
and 106.3 (quaternary carbons of p‐cymene), 128.6,
132.5, 135.2, 136.5 (CH), 162.2 (C=O), 172.8 (C=S),
179.5 (COOH). FT‐IR (KBr, cm−1): 3202 (m, ν (amide N‐
H)), 3132 (s, ν (thiourea N‐H)), 1659 (s, ν(C=O)), 1745
(s, ν (COOH)), 1194 (s, ν(C=S)). UV–vis [CHCl3; λ, nm
(ε, dm3mol−1 cm−1)]: 449 (6700), 335 (35000), 294
(76500), 255 (102900).
̶
̶1
vis [CHCl3; λ, nm (ε, dm3 mol cm )]: 444 (6600), 330
(30600), 254 (138100).
2.3.4 | [RuCl2(η6‐p‐cymene)L4] (4)
Yield: 81%, 183 mg. M.p.: 165 °C. [α]D27: +76°. Anal.
2.3.2 | [RuCl2(η6‐p‐cymene)L2] (2)
calcd for C19H24Cl2N2O3RuS2: C, 40.42; H, 4.29; N, 4.96;
1
Yield: 77%, 172 mg. M.p.: 166 °C. [α]D27: +78°. Anal.
S, 11.36. Found: C, 40.33; H, 4.15; N, 4.87; S, 11.25. H
calcd for C21H26Cl2N2O3RuS: C, 45.16; H, 4.69; N, 5.02;
S, 5.74. Found: C, 45.05; H, 4.55; N, 4.90; S, 5.62. H
NMR δ, ppm (500 MHz, DMSO‐d6): 1.18 (d, 6H,
J = 7.0 Hz, 2CH3 of p‐cymene), 1.48 (d, 3H, J = 7.2 Hz,
CH3 of the ligand), 2.09 (s, 3H, CH3 of p‐cymene), 2.84
(m, 1H, CH of p‐cymene), 4.83 (m, 1H, C*HMe),
5.77–5.83 (m, 4H, aromatic protons of p‐cymene),
7.23–8.36 (m, 3H, aromatic protons of the ligand), 11.15
(d, J = 7.0 Hz, 1H, C=S attached N‐H), 11.56 (s, 1H,
C=O and C=S attached N‐H), 13.20 (bs, 1H, COOH).
13C NMR δ, ppm (125 MHz, DMSO‐d6): 17.1 (CH3 of
the ligand), 17.8 (CH3 of p‐cymene), 21.4 (2CH3 of
p‐cymene), 29.9 (CH of p‐cymene), 53.0 (asymmetric
carbon), 85.4–86.3 (aromatic carbons of p‐cymene),
100.0 and 106.3 (quaternary carbons of p‐cymene),
128.6, 132.5, 135.2, 136.5 (CH), 162.2 (C=O), 172.8
(C=S), 179.5 (COOH). FT‐IR (KBr, cm−1): 3217 (m, ν
(amide N‐H)), 3153 (s, ν (thiourea N‐H)), 1673 (s,
ν(C=O)), 1741 (s, ν (COOH)), 1184 (s, ν(C=S)). UV–vis
[CHCl3; λ, nm (ε, dm3mol−1 cm−1)]: 448 (5900), 336
(32560), 293 (72825), 255 (102530).
1
NMR δ, ppm (500 MHz, DMSO‐d6): 1.19 (d, 6H,
J = 7.0 Hz, 2CH3 of p‐cymene), 1.49 (d, 3H, J = 7.2 Hz,
CH3 of the ligand), 2.08 (s, 3H, CH3 of p‐cymene), 2.83
(m, 1H, CH of p‐cymene), 4.84 (m, 1H, C*HMe),
5.76–5.81 (m, 4H, aromatic protons of p‐cymene),
7.50–7.94 (m, 5H, aromatic protons of the ligand), 11.29
(d, J = 7.0 Hz, 1H, C=S attached N‐H), 11.49 (s, 1H,
C=O and C=S attached N‐H), 13.20 (bs, 1H, COOH).
13C NMR δ, ppm (125 MHz, DMSO‐d6): 17.1 (CH3 of
the ligand), 17.8 (CH3 of p‐cymene), 21.4 (2CH3 of
p‐cymene), 29.9 (CH of p‐cymene), 53.0 (asymmetric car-
bon), 85.4–86.3 (aromatic carbons of p‐cymene), 100.0
and 106.3 (quaternary carbons of p‐cymene), 128.3,
128.5, 132.0, 133.0 (CH), 168.4 (C=O), 172.8 (C=S),
179.8 (COOH). FT‐IR (KBr, cm−1): 3211 (m, ν (amide N‐
H)), 3143 (s, ν (thiourea N‐H)), 1672 (s, ν(C=O)), 1729
(s, ν (COOH)), 1194 (s, ν(C=S)). UV–vis [CHCl3; λ, nm
(ε, dm3mol−1cm−1)]: 443 (8200), 329 (38500), 254
(173000).
2.3.5 | [RuCl2(η6‐p‐cymene)L5] (5)
Yield: 77%, 177 mg. M.p.: 158 °C. [α]D27: +60°. Anal.
2.3.3 | [RuCl2(η6‐p‐cymene)L3] (3)
calcd for C19H30Cl2N2O4RuS: C, 41.16; H, 5.45; N, 5.05;
1
Yield: 74%, 166 mg. M.p.: 164 °C. [α]D27: − 80°. Anal.
S, 5.78. Found: C, 41.05; H, 5.36; N, 4.93; S, 5.65. H
calcd for C19H24Cl2N2O3RuS2: C, 40.42; H, 4.29; N, 4.96;
S, 11.36. Found: C, 40.35; H, 4.19; N, 4.89; S, 11.26. H
NMR δ, ppm (500 MHz, DMSO‐d6): 1.19 (d, 6H,
J = 7.0 Hz, 2CH3 of p‐cymene), 1.48 (d, 3H, J = 7.2 Hz,
CH3 of the ligand), 2.09 (s, 3H, CH3 of p‐cymene), 2.84
(m, 1H, CH of p‐cymene), 4.82 (m, 1H, C*HMe), 5.77–
5.83 (m, 4H, aromatic protons of p‐cymene), 7.23–8.06
(m, 3H, aromatic protons of the ligand), 11.05 (d,
J = 7.0 Hz, 1H, C=S attached N‐H), 11.23 (s, 1H, C=O
and C=S attached N‐H), 13.20 (bs, 1H, COOH). 13C
NMR δ, ppm (125 MHz, DMSO‐d6): 17.1 (CH3 of the
1
NMR δ, ppm (500 MHz, DMSO‐d6): 1.18 (d, 6H,
J = 7.0 Hz, 2CH3 of p‐cymene), 1.48 (d, 3H, J = 7.2 Hz,
CH3 of the ligand), 2.09 (s, 3H, CH3 of p‐cymene), 2.84
(m, 1H, CH of p‐cymene), 4.83 (m, 1H, C*HMe),
5.77–5.83 (m, 4H, aromatic protons of p‐cymene),
7.23–8.36 (m, 3H, aromatic protons of the ligand), 11.15
(d, J = 7.0 Hz, 1H, C=S attached N‐H), 11.56 (s, 1H,

SHEEBA ET AL.
5 of 12
ligand), 17.8 (CH3 of p‐cymene), 21.4 (2CH3 of p‐
cymene), 29.9 (CH of p‐cymene), 53.0 (asymmetric car-
bon), 85.4–86.3 (aromatic carbons of p‐cymene), 100.0
and 106.3 (quaternary carbons of p‐cymene), 112.5,
118.4, 144.5, 148.3 (CH), 157.8 (C=O), 172.7 (C=S),
179.4 (COOH). FT‐IR (KBr, cm−1): 3223 (m, ν (amide N‐
H)), 3182 (s, ν (thiourea N‐H)), 1682 (s, ν(C=O)), 1743
(s, ν (COOH)), 1200 (s, ν(C=S)). UV–vis [CHCl3; λ, nm
stirred at 60 °C. After 20 hr, the reaction mixture was
cooled to room temperature, quenched with ice and then
extracted with dichloromethane. The extracts were dried
over Na2SO4, filtered, and passed through a silica gel
short column with n‐hexane‐ethyl acetate (1:1) eluent to
remove the Ru catalyst. The conversions were monitored
by GC–MS and GC analyses, and the enantiomeric
excesses were determined by using chiral HPLC.
̶
(ε, dm3mol−1 cm 1)]: 443 (6000), 333 (22700), 282 (72000).
3 | RESULTS AND DISCUSSION
2.3.6 | [RuCl2(η6‐p‐cymene)L6] (6)
3.1 | Formation of the ligands and
Yield: 83%, 180 mg. M.p.: 157 °C. [α]D27: − 54°. Anal. calcd
for C19H30Cl2N2O4RuS: C, 41.16; H, 5.45; N, 5.05; S, 5.78.
Found: C, 41.03; H, 5.37; N, 4.91; S, 5.67. 1H NMR δ, ppm
(500 MHz, DMSO‐d6): 1.19 (d, 6H, J = 7.0 Hz, 2CH3 of
p‐cymene), 1.48 (d, 3H, J = 7.2 Hz, CH3 of the ligand),
2.09 (s, 3H, CH3 of p‐cymene), 2.84 (m, 1H, CH of
p‐cymene), 4.82 (m, 1H, C*HMe), 5.77–5.83 (m, 4H, aro-
matic protons of p‐cymene), 7.23–8.06 (m, 3H, aromatic
protons of the ligand), 11.05 (d, J = 7.0 Hz, 1H, C=S
attached N‐H), 11.23 (s, 1H, C=O and C=S attached N‐
H), 13.20 (bs, 1H, COOH). 13C NMR δ, ppm (125 MHz,
DMSO‐d6): 17.1 (CH3 of the ligand), 17.8 (CH3 of
p‐cymene), 21.4 (2CH3 of p‐cymene), 29.9 (CH of
p‐cymene), 53.0 (asymmetric carbon), 85.4–86.3 (aromatic
carbons of p‐cymene), 100.0 and 106.3 (quaternary carbons
of p‐cymene), 112.5, 118.4, 144.5, 148.3 (CH), 157.8 (C=O),
172.7 (C=S), 179.4 (COOH). FT‐IR (KBr, cm−1): 3221 (m, ν
(amide N‐H)), 3182 (s, ν (thiourea N‐H)), 1682 (s, ν(C=O)),
1743 (s, ν (COOH)), 1200 (s, ν(C=S)). UV–vis [CHCl3; λ, nm
(ε, dm3mol−1 cm−1)]: 443 (5100), 333 (21400), 283 (69500).
complexes
The unprotected D/L‐alanine based aroylthiourea deriva-
tives (L1‐L6) were prepared (Scheme 1) and used for the
synthesis of chiral water soluble [RuCl2(p‐cymene)
(L1‐L6)] complexes (1–6) on reaction with [RuCl2(η6‐p‐
cymene)]2 in toluene (Scheme 2). The ligands and their
Ru‐p‐cymene complexes were characterized by using var-
ious spectroscopic (1H NMR, 13C NMR, FT‐IR and
UV–Vis) techniques and elemental analysis. The solid
state structure of L1, 5 and 6 was proven by single crystal
X‐ray diffraction analysis. The optical rotation value of
the compounds was determined from the polarimetric
study. All the synthesized compounds are stable in air
and soluble in aqueous and organic solvents.
3.2 | Structure of the ligands and
complexes
1
In the H NMR spectra of L1‐L6 (Figure S1–S6), a broad
singlet was observed in the chemical shift value of
13.08–13.52 ppm, which corresponds to the carboxyl O‐
H proton present in all the ligands. The C=S connected
N‐H, and C=O and C=S connected N‐H protons were
identified as doublet and singlet respectively in the region
11.08–11.49 ppm. The resonances due to the aromatic
protons appeared at 6.73–8.29 ppm in the spectra of the
aroylthiourea derivatives. The proton attached to the
2.4 | Procedure for asymmetric reduction
of ketones in water
To the [RuCl2(p‐cymene)(L1‐L6)] complex (1–6)
(0.005 mmol) in water (0.5 ml), HCOOH‐NEt3 (molar
ratio 1.0:5.1) mixture was added. Then ketone (1 mmol)
was introduced into the mixture and the solution was
SCHEME 1 Synthesis of the ligands
(L1‐L6)

6 of 12
SHEEBA ET AL.
1745 cm−1 in the spectra of the complexes confirmed
the presence of the acid group.[39] UV–visible spectra of
1–6 displayed d‐d and charge transfer transition bands
in the regions 443–449 and 329–336 nm, respectively;
which attested formation of the complexes. The bands
due to n‐π* and π‐π* transitions were observed in the
regions 283–294 and 251–257 nm, respectively.
The structure of L1, 5 and 6 was ascertained by XRD
studies and is shown in Figures 1–3. The experimental
parameters and crystal data are given in Table S1. The
structure of the complexes exposed monodentate sulfur
coordination mode of the aroylthiourea ligands and the
uncoordinated COOH group. The “3‐legged piano‐stool”
coordination geometry was present around Ru ion. The
hydrogen bonding interactions O(3)‐H(3)...S(1)#1 and
N(2)‐H(2)...O(1) (L1), and O(4)‐H(4)...Cl(1), N(1)‐H(1)...
Cl(2) and N(2)‐H(2)...O(1) (5 and 6), characteristic of
aroylthiourea and its Ru‐p‐cymene complex, respectively,
were perceived.[35,37] Bond lengths and angles were com-
parable with the literature values.[35,37]
SCHEME 2 Synthesis of the complexes (1–6)
chiral carbon was observed as a multiplet at 4.75–
4.85 ppm. The CH3 protons were detected as a singlet at
1.40–1.49 ppm. The broad signal witnessed at 13.2 ppm
1
3.3 | Asymmetric hydrogenation of
pro‐chiral ketones in water
due to carboxyl O‐H proton in the H NMR spectra of
the complexes (1–6) indicated the presence of D/L‐alanine
in the unprotected form (Figure S7‐S12). The existence of
p‐cymene in the complexes was confirmed from the new
signals appeared at 1.18–1.19, 2.08–2.09, 2.83–2.84 and
5.76–5.83 ppm (Figure S13–S18).[35,37] The chemical shift
values of CH3, C*H and aromatic protons of the complexes
were virtually comparable to those of the corresponding
ligands. The 13C NMR spectra of L1‐L6 contained signals
around 17.1–17.6 and 53.0–53.5 ppm (Figure S13–S18),
which were attributed to CH3 and asymmetric carbons
respectively. The aromatic ring carbons showed signals at
112.5–148.3 ppm. The C=O and C=S resonances were
noticed at 157.7–168.4 and 171.2–175.5 ppm correspond-
ingly. The signal pertaining to carboxylic acid was seen
at 179.4–180.0 ppm. There was no substantial alteration
in the 13C NMR spectra consequent to coordination of
the ligands with Ru (Figures S19–S24). The p‐cymene moi-
ety showed new signals at 17.8, 21.4, 29.9, 85.4, 86.3, 100.0
and 106.3 ppm in the spectra of the complexes.[35,37] In
general, the observed chemical shift values were consis-
tent with the literature values.[35,37]
The chiral water soluble [RuCl2(p‐cymene)(L1‐L6)] com-
plexes (1–6) were applied for the enantioselective hydro-
genation of aromatic ketones to produce their respective
alcohols in enantiopure form. The reactions were per-
formed with formic acid‐triethylamine mixture in water.
The effect of variables such as pH, temperature, solvent,
reaction time and catalyst amount was studied.
The ATH reaction was often accomplished in
isopropanol or the azeotropic mixture of HCOOH and
Further, the complex formation and coordination
mode of the aroylthiourea ligands were recognized from
the FT‐IR spectra. The C=O and amide N‐H stretching
frequencies were nearly unaffected upon complexation,
while the stretching frequency of the C=S decreased
from 1258–1283 to 1184–1200 cm−1, which proposed
monodentate coordination of the ligands to Ru ion
via the sulfur atom.[35,37,38] The carboxylic acid C=O
stretching frequency observed in the region 1729–
FIGURE 1 Thermal ellipsoidal plot of L1 showing the atomic
labeling scheme and thermal ellipsoids at the 50% probability
level. Selected bond distances (Å) and angles (°): S(1)‐C(1)
1.6774(18), O(1)‐C(2) 1.221(2), O(2)‐C(11) 1.206(2), O(3)‐H(3)
0.8400, O(3)‐C(11) 1.322(2), N(1)‐H(1) 0.8800, N(2)‐H(2) 0.8800,
C(1)‐N(1)‐H(1) 116.4, C(1)‐N(2)‐H(2) 118.6, N(1)‐C(1)‐S(1)
119.44(13), N(2)‐C(1)‐S(1) 123.59(13), N(2)‐C(1)‐N(1) 116.96(15),
O(1)‐C(2)‐N(1) 121.97(16)

SHEEBA ET AL.
7 of 12
crucial.[40–45] Very few reports explained the effect of pH
on the ATH.[46,47] For example, Noyori–Ikariya catalyst
exhibited pH‐dependent activity towards the ATH of
ketones in the presence of HCOOH‐NEt3 mixture in
water.[48] This stimulated us to study the effect of pH on
the ATH of ketones by varying the molar ratio of
HCOOH and NEt3, which gave interesting results
(Figure 4.). At pH = 8, maximum conversion (99%) was
obtained and hence the corresponding molar ratio of
HCOOH and NEt3 (1.0:5.1) was utilized in further exper-
iments. The influence of temperature on the reaction was
investigated (Figure 5.). The results revealed that lower
(30, 40 and 50 °C) temperatures were not favorable
whereas excellent conversion (99%) and ee (92%) were
observed at 60 °C. Further increase of temperature to
80 °C slightly decreased the conversion (95%) and ee
(88%). So the optimum temperature was 60 °C. To choose
the appropriate solvent/hydrogen donor, ATH of
acetophenone was carried out in 2‐propanol, water and
without solvent (neat) (Table 1.). When 2‐propanol was
used as solvent/hydrogen donor in the presence NaOH,
the conversion and ee were 83 and 94% respectively after
20 hr. Interestingly, the use of H2O as a solvent and
HCOOH‐NEt3 mixture as a hydrogen donor/base lead to
99% conversion and 92% ee after the same duration. In
the presence of HCOOH‐NEt3 mixture under the neat
condition (without H2O), only 81% of acetophenone was
converted into (S)‐1‐phenylethanol (77% ee) even after
24 hr. It was obvious from the results that HCOOH‐
NEt3/H2O combination was the best choice for the pres-
ent catalytic system. The ATH of acetophenone in water
was monitored at different time intervals. The maximum
FIGURE 2 Thermal ellipsoidal plot of 5 showing the atomic
labeling scheme and thermal ellipsoids at the 50% probability
level. Selected bond distances (Å) and angles (°): Ru(1)‐S(1)
2.3971(19), Ru(1)‐Cl(1) 2.439(2), Ru(1)‐Cl(2) 2.429(2), S(1)‐Ru(1)‐
Cl(1) 91.87(7), S(1)‐Ru(1)‐Cl(2) 89.83(7), Cl(2)‐Ru(1)‐Cl(1) 86.64(6),
C(1)‐S(1)‐Ru(1) 116.25(13)
FIGURE 3 Thermal ellipsoidal plot of 6 showing the atomic
labeling scheme and thermal ellipsoids at the 50% probability
level. Selected bond distances (Å) and angles (°): Ru(1)‐S(1)
2.3979(13), Ru(1)‐Cl(1) 2.4276(13), Ru(1)‐Cl(2) 2.4390(12), S(1)‐
Ru(1)‐Cl(1) 89.81(5), S(1)‐Ru(1)‐Cl(2) 91.93(5), Cl(1)‐Ru(1)‐Cl(2)
86.63(4), C(1)‐S(1)‐Ru(1) 116.18(18)
FIGURE 4 Effect of pH on conversion for the asymmetric
hydrogenation of acetophenone (1 mmol) using 1 as catalyst
(0.005 mmol) and HCOOH‐NEt3 (by varying the molar ratio from
1.0:13.0 to 1.0:4.7) as hydrogen donor in water (0.5 ml) at 60 °C for
20 hr
NEt3 in water. When HCOOH‐NEt3 mixture was used as
a reductant, ATH was found to be pH dependent and
hence the ratio of the amount of HCOOH and NEt3 was

8 of 12
SHEEBA ET AL.
FIGURE 5 Effect of temperature on conversion and ee for the
hydrogenation of acetophenone (1 mmol) in water (0.5 ml) using
catalyst 1 (0.005 mmol) and HCOOH‐NEt3 (molar ratio 1.0:5.1) after
20 hr
FIGURE 6 Effect of time and catalyst amount on conversion for
hydrogenation of acetophenone (1 mmol) in water (0.5 ml) using
catalyst 1 (0.005 mmol) and HCOOH‐NEt3 (molar ratio 1.0:5.1) at
60 °C
conversion and ee were achieved after 20 hr (Figure 6.).
The catalyst loading was optimized by using different
amount (0.001, 0.003, 0.005 and 0.007 mmol) of catalyst
1 towards ATH of acetophenone (Figure 6.). When
0.005 mmol of catalyst 1 was used, quantitative conver-
sion and excellent ee (99%) were reached.
the conversion was very much lower. Ru‐p‐cymene
dimer with sodium 2,2′‐((1R,2R)‐1‐amino‐2‐(4‐methyl-
phenylsulfonamido) ethane‐1,2‐diyl) dibenzene sulfonate
provided 99% conversion and 95% ee after 24 hr,[12] which
was comparable with the present catalysts (1–6). Ru‐p‐
cymene‐TsDPEN (TsDPEN = N‐(p‐toluenesulfonyl)‐1,2‐
Asymmetric reduction of various aromatic ketones to
their respective enantiopure alcohols was demonstrated
using chiral Ru (II)‐p‐cymene catalysts (1–6) in water in
the presence of HCOOH‐NEt3 at 60 °C. Excellent conver-
sion and optical purity were attained within 20 hr for
acetophenone, 24 hr for 4‐methoxy benzophenone
and 22 hr for other substituted ketones (Table 2.). The
effectiveness of the current asymmetric catalytic system
was compared with that of the recognized Ru‐p‐cymene
catalysts, specifically with attention to the ATH of
acetophenone in water (Scheme 3). Asymmetric reduction
of acetophenone with Ru‐η6‐p‐cymene dimer and (R)‐N‐
(4‐fluorophenyl)pyrrolidine‐2‐carboxamide proceeded for
18 hr to show 98% conversion and 67% ee.[14] Though
the conversion was comparable with the present
system, ee was significantly lower. The combination of
[RuCl2(p‐cymene)]2 and N‐((1S,2S)‐2‐amino‐1,2‐bis(2‐
diphenyl‐ethylenediamine)
demonstrated
superior
results (conversion 99% and ee 94%) within 12 hr.[11]
Ru (II)‐p‐cymene complex containing N‐((1S,2S)‐2‐
aminocyclohexyl)‐4‐methylbenzenesulfonamide or (−)‐
ephedrine hydrochloride catalyzed asymmetric reduction
of acetophenone efficiently in water medium, which was
comparable with our catalytic system.[21,30] It is clear from
the comparison that the Ru‐p‐cymene organometallic
compounds reported in this paper are among the few effec-
tive catalysts for ATH of ketones in water.
The synthesis of optically pure enantiomer of
substituted aromatic alcohols is very important as
they can be used as chiral building blocks for many
pharmaceuticals such as L‐chlorprenaline, R‐tomoxetine,
S‐fluoxetine, R‐salbutamol, S‐duloxetine and R‐
aminophenyl)
ethyl)‐4‐methylbenzene
sulfonamide
offered 33% conversion and 95% ee within 1 hr[5]; ee was
comparable with that produced by 1, 3, 4, 5 and 6, but
TABLE 1 Optimization of hydrogen donor
Catalyst 1
(mg)
Conversion
(%)
ee
(%)
Entry
Solvent
H‐Donor
1a
2b
3c
3.5
3.5
3.5
2‐propanol
H2O
2‐propanol/NaOH
HCOOH/NEt3
HCOOH/NEt3
83
99
81
94
92
77
Neat
a0.005 mmol of 1 in 5 ml of 2‐propanol, 1 mmol of NaOH and 1 mmol of acetophenone at 80 °C, for 20 hr.
b0.005 mmol of 1 in 0.5 ml of water, HCOOH:NEt3 (molar ratio 1.0:5.1) and 1 mmol of acetophenone at 60 °C for 20 hr.
c0.005 mmol of 1, HCOOH:NEt3 (molar ratio 1.0:5.1) and 1 mmol of acetophenone at 60 °C for 24 hr.

SHEEBA ET AL.
9 of 12
TABLE 2 Enantioselective reduction of ketones catalyzed by Ru (II) complexes (1–6)a
Entry
Catalyst
Substrate
Product
Conversionb (%)
eec (%) /Configurationd
TONe
1
2
3
4
5
6
1
2
3
4
5
6
99
99
99
82
81
83
92/S
76/S
98/S
93/S
91/S
94/S
198
198
198
164
162
166
7
8
9
10
11
12
1
2
3
4
5
6
63
73
61
98
95
97
86/R
97/R
98/R
97/R
91/R
97/R
126
146
122
196
190
194
13
14
15
16
17
18
1
2
3
4
5
6
91
94
98
79
91
98
70/S
63/S
90/R
94/R
94/R
90/R
181
188
196
158
182
196
19
20
21
22
23
24
1
2
3
4
5
6
97
94
74
99
99
97
73/R
84/S
78/S
91/S
76/S
66/S
194
188
148
198
198
194
25
26
27
28
29
30
1
2
3
4
5
6
64
57
69
54
75
62
68/R
66/R
96/S
75/R
90/R
84/S
128
114
138
108
150
124
31
32
33
34
35
36
1
2
3
4
5
6
98
99
99
99
97
99
99/R
99/S
99/R
99/S
99/R
99/R
196
198
198
198
194
198
aReactions were carried out at 60 °C using 1 mmol of ketone, 0.005 mmol of Ru (II)‐p‐cymene complex in 0.5 ml of water and HCOOH:NEt3 (molar ratio 1.0:5.1)
for 20–24 hr.
bThe conversion was determined by GC–MS.
cee was determined by chiral HPLC.
dAbsolute configuration was determined from the optical rotation values.
eTON = moles of the product formed/moles of the catalyst used.
denopamine.[49–56] 2‐Methyl acetophenone was trans-
formed into (R)‐1‐(2‐methylphenyl) ethanol with 98%
conversion and 98% ee (Table 2, entries 7–12). The cata-
lysts (1–6) were used for the conversion (up to 98%) of
4‐fluoro acetophenone to 4‐fluorophenylethanal (up to
94% ee) (Table 2, entries 13–18). The enantioselective
reduction of heterocyclic ketone, 1‐(2‐furanyl)‐ethanone,
was successful in our method which offered 1‐(furan‐2‐
yl) ethanol with 99% conversion and 91% ee using catalyst
4 (Table 2, entries 19–24). Using the present catalytic
system, chiral benzhydrol was derived from a bulky
ketone, 4‐methoxy benzophenone (Table 2, entries
25–30). 2‐Hydroxy acetophenone was converted in to
2‐(1‐hydroxyethyl) phenol in 99% conversion and 99% ee

10 of 12
SHEEBA ET AL.
SCHEME 3 Conversion and ee
obtained from reported chiral ligands with
[RuCl2(η6‐p‐cymene)]2 in water
(Table 2, entries 31–36). ATH of aliphatic and cyclic
ketones was not successful with the present reaction
conditions.
presented in Figure 7.[34,58,59] The similar concerted
mechanism was proposed for our previous system and
confirmed by experimental and theoretical studies.[37,38]
The Ru‐hydride species which formed after the exposure
of the catalyst with HCOOH‐NEt3 interacted with the
ketone substrate through the Ru‐H and N‐H units to form
a cyclic six‐membered transition state that delivered
enantiopure secondary alcohols. The rate of the hydroge-
nation reaction increases at pH values greater than 4,
which could be due to the improved concentration of
HCOO−. At pH > 4, HCOOH (pKa = 3.7) stays predomi-
nately as HCOO−, which is desirable to form the ruthe-
nium formato complex. The configuration of product
alcohols did not depend on that of the complexes in most
of the cases. This may be due to the fact that only diaste-
reomers (resulting from chiral centered Ru) with equal
configuration might be active.[37]
3.4 | Plausible mechanism
The homogeneous ATH of pro‐chiral ketones to the
respective chiral secondary alcohols might follow the
concerted mechanism proposed by Noyori et al.,[57] and
explained by Wu et al.[23] Presently, the catalysis proceeds
under basic condition and the possible mechanism is
4 | CONCLUSIONS
The chiral water soluble [RuCl2(p‐cymene)(L1‐L6)] com-
plexes (1–6) obtained from the reaction between Ru
(II)‐η6‐p‐cymene dimer and the chiral D/L‐alanine‐
aroylthiourea derivatives (L1‐L6) were characterized. In
all the complexes, aroylthiourea exhibited monodentate
sulfur coordination with Ru ion. All the complexes
(1–6) demonstrated high catalytic activity towards the
asymmetric reduction of aromatic ketones to the respec-
tive chiral secondary alcohols in water. The water
medium and non‐inert atmospheric condition made the
present system of enantioselective reduction of aromatic
ketones eco‐friendly and simple. To add, the efficiency
of the catalytic system is comparable to superior systems.
The encouraging results of ATH may prompt the scien-
tists to use these catalysts for other asymmetric reactions
in water medium.
FIGURE
7
Proposed catalytic cycle for asymmetric
hydrogenation of ketones under acidic and basic conditions

SHEEBA ET AL.
11 of 12
[23] X. Wu, X. Li, F. King, J. Xiao, Angew. Chem. Int. Ed. 2005, 44,
ACKNOWLEDGMENTS
3407.
M. M. S. thankfully acknowledges the Department of Sci-
ence and Technology, Ministry of Science and Technol-
ogy, Government of India, for the fellowship under
DST‐INSPIRE scheme. We acknowledge Dr. S. Velmathi,
NIT, Trichy, for optical rotation studies.
[24] C. A. Madrigal, A. Garcia‐Fernandez, J. Gimeno, E. Lastra,
J. Organomet. Chem. 2008, 693, 2535.
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[26] X. Zhou, X. Wu, B. Yang, J. Xiao, J. Mol. Catal. A: Chem. 2012,
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ORCID
[27] W. Wang, Q. Wang, Chem. Commun. 2010, 46, 4616.
[28] I. D. Gridnev, Y. Yamanoi, N. Higashi, H. Tsuruta, M.
Manoharan Muthu Tamizh
0673-5177
https://orcid.org/0000-0002-
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How to cite this article: Sheeba MM, Tamizh
MM, Bhuvanesh NSP, Karvembu R. Water soluble
Ru (II)–p‐cymene complexes of chiral
aroylthiourea ligands derived from unprotected
D/L‐alanine as proficient catalysts for asymmetric
transfer hydrogenation of ketones. Appl
Organometal Chem. 2018;e4667. https://doi.org/
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