Synthesis and Structures of Arene Ruthenium (II)–NHC Complexes: Efficient Catalytic α-alkylation of ketones via Hydrogen Auto Transfer Reaction

Article abstract of DOI:10.1002/aoc.4696

A panel of six new arene Ru (II)-NHC complexes 2a-f, (NHC?=?1,3-diethyl-(5,6-dimethyl)benzimidazolin-2-ylidene 1a, 1,3-dicyclohexylmethyl-(5,6-dimethyl)benzimidazolin-2-ylidene 1b and 1,3-dibenzyl-(5,6-dimethyl)benzimidazolin-2-ylidene 1c) were synthesized from the transmetallation reaction of Ag-NHC with [(η⁶-arene)RuCl₂]₂ and characterized. The ruthenium (II)-NHC complexes 2a-f were developed as effective catalysts for α-alkylation of ketones and synthesis of bioactive quinoline using primary/amino alcohols as coupling partners respectively. The reactions were performed with 0.5?mol% catalyst load in 8?h under aerobic condition and the maximum yield was up to 96%. Besides, the different alkyl wingtips on NHC and arene moieties were studied to differentiate the catalytic robustness of the complexes in the transformations.

Full text of DOI:10.1002/aoc.4696

Received: 6 September 2018
DOI: 10.1002/aoc.4696
Revised: 15 October 2018
Accepted: 16 October 2018
F U L L P A P E R
Synthesis and Structures of Arene Ruthenium (II)–NHC
Complexes: Efficient Catalytic α‐alkylation of ketones via
Hydrogen Auto Transfer Reaction
Gunasekaran Balamurugan1 | Sundarraman Balaji1 | Rengan Ramesh1
Nattamai S.P. Bhuvanesh2
|
1 Centre for organometallic Chemistry,
A panel of six new arene Ru (II)‐NHC complexes 2a‐f, (NHC = 1,3‐diethyl‐(5,6‐
dimethyl)benzimidazolin‐2‐ylidene 1a, 1,3‐dicyclohexylmethyl‐(5,6‐dimethyl)
benzimidazolin‐2‐ylidene 1b and 1,3‐dibenzyl‐(5,6‐dimethyl)benzimidazolin‐
2‐ylidene 1c) were synthesized from the transmetallation reaction of Ag‐NHC
with [(η6‐arene)RuCl2]2 and characterized. The ruthenium (II)‐NHC complexes
2a‐f were developed as effective catalysts for α‐alkylation of ketones and syn-
thesis of bioactive quinoline using primary/amino alcohols as coupling part-
ners respectively. The reactions were performed with 0.5 mol% catalyst load
in 8 h under aerobic condition and the maximum yield was up to 96%. Besides,
the different alkyl wingtips on NHC and arene moieties were studied to differ-
entiate the catalytic robustness of the complexes in the transformations.
School of Chemistry, Bharathidasan
University, Tiruchirapalli
620024Tamilnadu, India
2 Department of Chemistry, Texas A&M
University, College Station, Texas 77842‐
3012, USA
Correspondence
Rengan Ramesh, Centre for
organometallic Chemistry, School of
Chemistry, Bharathidasan University,
Tiruchirapalli, 620024, Tamilnadu, India.
Email: ramesh_bdu@yahoo.com
Funding information
Council of Scientific and Industrial
Research, Grant/Award Number:
02(0142)/13/EMR‐II
KEYWORDS
acceptorless dehydrogenation, arene Ru‐NHC, borrowing hydrogen, quinoline synthesis, α‐
Alkylation
1 | INTRODUCTION
methodology simply involves, the alcohol oxidation to
aldehyde in the presence of metal catalysts followed by
Construction of new carbon–carbon and carbon‐nitrogen
bonds using transition metal complexes is an indispens-
able catalytic tool in synthetic organic chemistry.[1] How-
ever, several methodologies were developed for the
transformation, especially the α‐alkylation of carbonyl
compounds is one of the significant and/or alternative
routes for the construction of new C‐C bonds.[2] Tradi-
tionally, alkylation process performed with alkyl halide
as an alkylating source in the presence of a stoichiometric
amount of base is a high cost process, that leads to a
desired product with the formation of toxic waste limiting
its sustainable applications.[3] Therefore, a necessary driv-
ing force for the sustainable development of new method-
ology through hydrogen borrowing or hydrogen auto
transfer process is mandatory with the aid of transition
metal catalysts and alcohols as alkylating agent.[4] This
condensation with ketone to form a α,β‐unsaturated
ketone intermediate, further which underwent C=C
reduction by metal‐hydride to offer reduced alkylated
ketone with the release of water as a side‐product
(Scheme 1).[5]
In fact, the metal‐catalyzed hydrogen‐borrowing strat-
egy provides prominence benefit including high atom
efficiency, low cost, water as by‐product etc., than other
methods.[6] Recently, the core moiety of the pharmaceuti-
cally active intermediate was successively synthesized
through hydrogen auto‐transfer process.[7] Further, some
of the late transition metal complexes containing Ru, Ir,
Rh, Pd, Fe and Co etc., were accounted as catalysts in
α‐alkylation of carbonyl compounds..[8]
In this connection, a large number of ruthenium
based catalysts was widely encountered in this area.
Appl Organometal Chem. 2018;e4696.
wileyonlinelibrary.com/journal/aoc
© 2018 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4696

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BALAMURUGAN ET AL.
in 48 hr [A].[11] Further, Glorius and co‐workers brought
the α‐alkylation chemistry forward by achieving the one‐
pot synthesis of donepezil drug and also providing a wide
number of branched product of ketones in an excellent
yield using 2 mol% of Ru (II)(NHC)2 for 24 hr [B].[12]
Also, more recently Zhu and co‐workers received a good
achievement in α‐alkylation of ketones with 0.5 mol% of
ruthenium NNN pincer type of complexes under argon
atmosphere for broad substrate scope of ketones and alco-
hols [C]..[13]
SCHEME 1 Metal‐catalysed hydrogen borrowing methodology
for α‐alkylation reactions
Amongst, the catalytic chemistry of arene‐ruthenium
(NHC) system having much impact with the same con-
cepts, inclusive coupling of alcohols and amine to
alkylated amine and amides, transfer hydrogenation
etc.[14] We envisioned that, 5,6‐dimethylbenzimidazolin‐
2‐ylidene ligands were used in catalysis and bioinorganic
chemistry.[15–17] It has also been proved that,
benzanulated NHCs derived from benzimidazolium pre-
cursor exhibiting interesting properties due to their inter-
mediate position between saturated and unsaturated
analogue.[18]
Though several metal catalysts are known for the
alkylation of ketones and synthesis of quinolines, the
reactions suffer from high catalyst loading, long reaction
time and addition of additives or oxidizing agents. On
the basis of previous literature, it is inferred that arene
Ru (II)‐NHC complexes of 5,6‐dimethylbenzimidazolin‐
2‐ylidene as catalysts for the alkylation of ketones with
alcohols remains rarely explored. In our continual efforts
for the development of new transition metal catalyzed
coupling reactions,[19] herein we attributed to execute
the alkylation reaction of ketones with arene Ru (II)‐
NHC complexes as catalysts. Further, the catalytic perfor-
mance of present complexes was extended to synthesize
quinoline derivatives via acceptorless dehydrogenative
Exclusively, Cho and co‐workers carried out the α‐
alkylation process using RuCl2(PPh3)2 using 1‐dodececne
as a hydrogen acceptor. Yus group also has reported
RuCl2(DMSO)4 precursor as a catalyst for the same reac-
tion using benzyl alcohol as an alkylating source with
stoichiometric amount of base. After a long time, Ryu
and co‐workers investigated the RuHCl (CO)(PPh3)3 cata-
lyst to catalyze the α‐alkylation reaction of ketones to cor-
responding alkylated products with 2 mol% Cs2CO3 at
140 °C, in the meanwhile Zhang group has also experi-
enced this field of chemistry with 1 mol% of [Ru(p‐
cymene)Cl2]2 along with xantphos as an additive in the
presence of t‐BuOK base to provide an array of α‐
pyridylated acetophenone products in good yield.[9] How-
ever, several transition metal complexes were attempted
well in this field of chemistry. In this regard, the metal
complexes have a strong sigma donor ligand like N‐
heterocyclic carbenes were found to be effective in the
borrowing hydrogen strategy.[10] Particularly, ruthenium
NHC based catalysts provide the most significant contri-
bution in this type of reactions as represented in
Scheme 2. Song et al. attained the α‐alkylated products
from the cross coupling reaction of primary and second-
ary alcohols using 2 mol% of protic Ru (II) NHC catalyst
SCHEME 2 Synthetic strategy of α‐
alkylation reactions using Ru (II) NHC
and pincer catalysts

BALAMURUGAN ET AL.
3 of 13
coupling of 2‐aminobenzyl alcohol and ketone. It is worth
to note that the present protocol works well with low cat-
alyst loading in shorter reaction time without external
additives.
2.4 | 1,3‐dibenzyl‐(5,6‐dimethyl)
benzimidazolium bromide 1c15c
5,6‐dimethylbenzimidazole (146.19 mg, 1 mmol), benzyl
bromide (342.06 mg, 2 mmol) K2CO3(138.21 mg, 1 mmol)
were mixed with 10 ml of dried CH3CN in a pressure tube
and stirred at 80 °C for 16 hr. Colour: white solid. Yield:
390 mg, 90.81%. Anal. Calcd. For C23H23BrN2
(407.35 g mol−1): C, 67.82; H, 5.69; N, 6.88. Found: C,
2 | EXPERIMENTAL SECTION
2.1 | General procedure for the synthesize
of ligand precursors (1a‐c)
1
67.26; H, 5.38; N, 6.56. H NMR (400 MHz, CDCl3): δ
(ppm) = 11.58 (s, 1H, CazoliumH), 7.48(t, J = 1.6 Hz, 4H,
CarH), 7.40–7.34 (m, 6H, CarH), 7.28(d, J = 4.4 Hz, 2H),
5.81(s, 4H) 2.33(s, 6H). 13C{1H} NMR (100 MHz, CDCl3):
δ (ppm) = 141.9, 137.4, 132.8, 129.9, 129.4, 129.2, 128.1,
113.3, 51.3, 20.7.
5,6‐dimethylbenzimidazole (1 mmol), alkyl bromide
(2 mmol) and K2CO3 (1 mmol) were mixed with 10 ml
of dried CH3CN in a pressure tube and stirred at 80 °C
for 16 hr. The reaction progress was monitored by TLC.
Further, the volume of the reaction mixture was reduced
up to 5 ml, then adding pet.ether to form a large amount
of precipitate, which was filtered and washed with pet.
ether for several times to obtain analytically pure product
as colourless solid with the yield of 70–90%.
2.5 | General procedure for the synthesis
of arene Ru (II) NHC complexes (2a‐f)
In a round bottom flask, Silver(I) oxide (0.1 mmol) and
ligand precursor (0.2 mmol) were dissolved in dried
dichloromethane (12 ml). The reaction mixture was
stirred for 6 hr at room temperature in the absence of
light and filtered through a celite plug to remove the sil-
ver halide. After that, [Ru (arene)Cl2]2 (0.1 mmol) was
added to the reaction mixture and stirred at room tem-
perature for 4 hr. The formation of complex was con-
firmed by monitoring TLC. The resulting brown
solution was filtered with celite plug and reduced to
5 ml under vacuum. Addition of petroleum ether into
the reaction mixture forms a brown precipitate. This
precipitate was filtered and purified by chromatography
using silica gel (60–120 mesh) as a packing material and
the eluents are CHCl3/CH3OH in 3:1 ratio to obtain
analytically pure product as brown solid 2a‐f in good
to an excellent yield (70–90%).
2.2 | 1,3‐diethyl‐(5,6‐dimethyl)
benzimidazolium bromide 1a
5,6‐dimethylbenzimidazole (146.19 mg, 1 mmol), ethyl
bromide (217.94 mg, 2 mmol) and K2CO3 (138.21 mg,
1 mmol) were mixed with 10 ml of dried CH3CN in a
pressure tube and stirred at 80 °C for 16 hr. Colour: white
solid. Yield: 199 mg,70.32%. Anal. Calcd. For C13H19BrN2
(283.21 g mol−1): C, 55.13; H, 6.76; N, 9.89. Found: C,
1
54.99; H, 6.31; N, 6.69. H NMR (400 MHz, CDCl3): δ
(ppm) = 11.21 (s, 1H, CazoliumH), 7.39 (s, 2H, CarH),
4.56 (q, J = 7.2 Hz, 4H), 2.41 (s, 6H), 1.64 (t, J = 7.2 Hz,
6H). 13C{1H} NMR (100 MHz, CDCl3): δ (ppm) = 140.6,
137.3, 129.7, 112.7, 42.7, 20.7, 14.9.
2.3 | 1,3‐dicyclohexylmethyl‐(5,6‐
dimethyl) benzimidazolium bromide 1b
2.6 | Dichloro[1,3‐diethyl‐(5,6‐dimethyl)‐
benzimidazolin‐2‐ylidene](benzene)
ruthenium (II) 2a
5,6‐dimethylbenzimidazole (146.19 mg, 1 mmol) and
cyclohexylmethyl bromide (354.16 mg, 2 mmol) were
mixed with 10 ml of dried CH3CN in a pressure tube
and stirred at 80 °C for 16 hr. Colour: white solid. Yield:
350 mg, 83.44%. Anal. Calcd. For C23H35BrN2
(419.44 g mol−1): C, 65.86; H, 8.41; N, 6.68. Found: C,
Transmetalation reaction was performed in CH2Cl2
(12 ml) with Silver(I) oxide (23.17 mg, 0.1 mmol), 1,3‐
diethyl‐(5,6‐dimethyl) benzimidazolium bromide (1a;
56.64 mg, 0.2 mmol), [Ru (benzene)Cl2]2 (50.02 mg,
0.1 mmol). Colour: brown. Yield: 40 mg, 88.11%. Anal.
Calcd. For C19H24Cl2N2Ru (452.38 g mol−1): C, 50.44; H,
1
65.41; H, 8.20; N, 6.43. H NMR (400 MHz, CDCl3): δ
(ppm) = 11.25 (s, 1H, CazoliumH), 7.41 (s, 2H, CarH),
4.42 (d, J = 7.6 Hz, 4H), 2.48 (s, 6H), 2.02(t,
J = 11.6 Hz, 2H), 1.91–1.60 (m, 10H), 1.28–1.13 (m,
10H). 13C{1H} NMR (100 MHz, CDCl3): δ (ppm) = 137.2,
130.0, 112.8, 53.0, 37.7, 30.3, 25.7, 25.3, 20.7.
1
5.35; N, 6.19. Found: C, 50.07; H, 5.21; N, 6.13. H NMR
(400 MHz, CDCl3): δ (ppm) = 7.21 (s, 2H, CarH), 5.6 (s,
6H, CbenzeneH), 4.73 (t, J = 7.2 Hz, 4H), 2.41 (s, 6H),
1.55 (t, J = 7.2 Hz, 6H).13C{1H} NMR (100 MHz, CDCl3):

4 of 13
BALAMURUGAN ET AL.
δ (ppm) = 183.0 (CcarbeneRu), 133.6, 132.0, 111.3, 111.1,
86.9, 86.7, 44.4, 20.4, 20.3, 16.0. ESI‐MS: m/z = 417.0664
(M‐Cl)+ (calcd m/z = 417.0666).
0.1 mmol). Colour: brown. Yield: 42 mg, 82.67%. Anal.
Calcd. For C23H32Cl2N2Ru (508.49 g mol−1): C, 54.33; H,
6.34; N, 5.51. Found: C, 53.87; H, 6.19; N, 5.35. H NMR
1
(400 MHz, CDCl3): δ (ppm) = 7.14(s, 2H, CarH), 5.41(t,
J = 6 Hz, 2H, CarH), 5.04 (d, J = 6 Hz, 2H, CarH),
4.90(q, J = 6 Hz, 2H, CarH), 4.32(q, J = 6.4 Hz, 2H, CarH),
2.98–2.87 (m, 1H), 2.33(s, 6H), 1.89(s, 3H), 1.51(t,
J = 7 Hz, 6H), 1.19(d, J = 7.2 Hz, 6H). 13C{1H} NMR
(100 MHz, CDCl3): δ (ppm) = 185.5 (CcarbeneRu), 133.7,
131.7, 111.1, 109.6, 99.4, 86.3, 82.7, 44.7, 30.6, 22.5,
20.3,18.6,16.1. ESI‐MS: m/z = 473.1292 (M‐Cl)+ (calcd
m/z = 473.1298).
2.7 | Dichloro[1,3‐dicyclohexylmethyl‐(5,6‐
dimethyl)‐benzimidazolin‐2‐ylidene]
(benzene) ruthenium (II) 2b
Transmetalation reaction was performed in CH2Cl2
(12 ml) with Silver(I) oxide (23.17 mg, 0.1 mmol), 1,3‐
dicyclohexylmethyl‐(5,6‐dimethyl) benzimidazolium bro-
mide (1b; 83.89 mg, 0.2 mmol), [Ru (benzene)Cl2]2
(50.02 mg, 0.1 mmol). Colour: brown. Yield: 50 mg,
84.60%. Anal. Calcd. For C29H40Cl2N2Ru (588.62 g mol
−1): C, 59.17; H, 6.85; N, 4.76. Found: C, 58.72; H, 6.72;
2.10 | Dichloro[1,3‐dicyclohexylmethyl‐
(5,6‐dimethyl)‐benzimidazolin‐2‐ylidene]
(p‐cymene) ruthenium (II) 2e
1
N, 4.59. H NMR (400 MHz, CDCl3): δ (ppm) = 7.07 (s,
2H, CarH), 5.61 (s, 6H, CbenzeneH), 4.63 (q, J = 4.8 Hz,
2H), 4.23 (q, J = 8.8 Hz, 2H), 2.30 (s, 6H), 2.01 (t,
J = 7.6 Hz, 2H), 1.74–1.61 (m, 8H), 1.35–1.05 (m, 8H),
0.91–0.86 (m, 4H). 13C{1H} NMR (100 MHz, CDCl3): δ
(ppm) = 185.8 (CcarbeneRu), 134.1, 131.6, 111.9, 86.6,
55.6, 38.0, 31.4, 30.9, 26.4, 26.1, 20.3, 1.05. ESI‐MS:
m/z = 553.4167 (M‐Cl)+ (calcd m/z = 553.1918).
Transmetalation reaction was performed in CH2Cl2
(12 ml) with Silver(I) oxide (23.17 mg, 0.1 mmol), 1,3‐
dicyclohexylmethyl‐(5,6‐dimethyl) benzimidazolium bro-
mide (1b; 83.89 mg, 0.2 mmol), [Ru(p‐cymene)Cl2]2
(61.24 mg, 0.1 mmol). Colour: brown. Yield: 56 mg,
86.96%. Anal. Calcd. For C33H48Cl2N2Ru (644.72 g mol
−1): C, 61.48; H, 7.50; N, 4.35. Found: C, 61.13; H, 7.05;
1
N, 4.27. H NMR (400 MHz, CDCl3): δ (ppm) = 7.27(s,
2.8 | Dichloro[1,3‐dibenzyl‐(5,6‐dimethyl)‐
benzimidazolin‐2‐ylidene] (benzene)
ruthenium (II) 2c
2H, CarH), 5.46(d, J = 6 Hz, 2H, CarH), 4.99(d,
J = 6 Hz, 4H, CarH) 4.03(s, 2H, CarH), 3.09–2.98(m, 1H),
2.41(s, 6H), 2.22(d, J = 21.2 Hz, 2H), 1.78(s, 3H), 1.63(s,
6H), 1.33–1.16 (m, 20H). 13C{1H} NMR (100 MHz,
CDCl3): δ (ppm) = 185.7(CcarbeneRu), 134.6, 131.3, 111.6,
108.4, 98.1, 87.5, 83.0, 54.3, 38.6, 31.6, 30.6, 29.1, 26.3,
26.0, 22.5, 20.4, 18.3. ESI‐MS: m/z = 609.2541 (M‐Cl)+
(calcd m/z = 609.2544).
Transmetalation reaction was performed in CH2Cl2
(12 ml) with Silver(I) oxide (23.17 mg, 0.1 mmol), 1,3‐
dibenzyl‐(5,6‐dimethyl) benzimidazolium bromide (1c;
81.47 mg, 0.2 mmol), [Ru (benzene)Cl2]2 (50.02 mg,
0.1 mmol). Colour: brown. Yield: 90 mg, 72.58%. Anal.
Calcd. For C29H28Cl2N2Ru (576.52 g mol−1): C, 60.42; H,
1
2.11 | Dichloro[1,3‐dibenzyl‐(5,6‐
dimethyl)‐benzimidazolin‐2‐ylidene](p‐
cymene) ruthenium (II) 2f
4.90; N, 4.86. Found: C, 60.01; H, 4.69; N, 4.75. H NMR
(400 MHz, CDCl3): δ (ppm) = 7.31–7.20(m, 6H, CarH),
7.01(d, J = 5.6 Hz, 4H, CarH), 6.87(d, J = 19.6 Hz, 4H),
5.46(d, J = 16.4 Hz, 2H, CarH), 5.12 (s, 6H, CbenzeneH),
2.2(s, 6H). 13C{1H} NMR (100 MHz, CDCl3):
δ
Transmetalation reaction was performed in CH2Cl2
(12 ml) with Silver(I) oxide (23.17 mg, 0.1 mmol), 1,3‐
dibenzyl‐(5,6‐dimethyl) benzimidazolium bromide (1c;
81.47 mg, 0.2 mmol), [Ru(p‐cymene)Cl2]2 (61.24 mg,
0.1 mmol). Colour: brown. Yield: 57 mg, 90.10%. Anal.
Calcd. For C33H36Cl2N2Ru (632.63 g mol−1): C, 62.65;
(ppm) = 186.6 (CcarbeneRu), 138.4, 134.4, 132.9, 129.2,
127.5, 125.5, 111.5, 86.4, 51.7, 20.3. ESI‐MS:
m/z = 541.0975 (M‐Cl)+ (calcd m/z = 541.0979).
1
H, 5.74; N, 4.43. Found: C, 62.19; H, 5.63; N, 4.22. H
2.9 | Dichloro[1,3‐diethyl‐(5,6‐dimethyl)‐
benzimidazolin‐2‐ylidene] (p‐cymene)
ruthenium (II) 2d
NMR (400 MHz, CDCl3): δ (ppm) = 7.37(t, J = 7.4 Hz,
4H, CarH), 7.30(d, J = 7.2 Hz, 2H, CarH) 7.12(d,
J = 7.2 Hz, 4H, CarH), 6.80(s, 2H, CarH), 6.56 (d,
J = 17.2 Hz, 2H, CarH), 5.73(d, J = 16.8 Hz, 2H, CarH),
5.31(d, J = 4.8 Hz, 2H, CarH), 5.01(d, J = 6 Hz, 2H),
2.70–2.63(m, 1H), 2.19(s, 6H), 1.84(s, 3H), 1.15 (d,
J = 6.8 Hz, 6H). 13C{1H} NMR (100 MHz, CDCl3): δ
Transmetalation reaction was performed in CH2Cl2
(12 ml) with Silver(I) oxide (23.17 mg, 0.1 mmol), 1,3‐
diethyl‐(5,6‐dimethyl) benzimidazolium bromide (1a;
56.54 mg, 0.2 mmol), [Ru(p‐cymene)Cl2]2 (61.24 mg,

BALAMURUGAN ET AL.
5 of 13
(ppm) = 189.1 (CcarbeneRu), 137.8, 134.2, 132.3, 128.9,
127.3, 125.9, 111.8, 107.5, 97.1, 85.2, 84.6, 52.6, 30.6,
22.5, 20.2, 18.2. ESI‐MS: m/z = 597.1600 (M‐Cl)+ (calcd
m/z = 597.1605).
corresponding benzimidazole was accomplished by the
reaction
of
anhydrous
K2CO3
with
5,6‐
dimethylbenzimidazole in acetonitrile medium and
followed by the addition of alkyl halide in stoichiometric
amount under the refluxing condition for 16 hr, resulted
in the formation of corresponding benzimidazolium salt
1a‐c with 70–90% yield. The suitable ligand precursor
2.12 | General procedure for the
α‐alkylation of ketone reactions
1
was primarily confirmed by H and 13C NMR spectros-
1
copy for complexation. Accordingly, the H NMR spectra
Ketones (0.5 mmol), alcohols (0.5 mmol), catalyst 2a
(2.26 mg, 0.5 mol%), NaOH (8 mg, 0.2 equiv) and toluene
(2 ml) were charged into a round neck flask and heated at
105 °C for 8 hr. The progress of the reaction was moni-
tored by TLC. Upon completion, the solvent was evapo-
rated and the residue was purified by column
chromatography over silica gel (60–120 mesh) with
hexane/ethyl acetate (95:5) mixture as eluent.
showed a sharp singlet at 10–11 ppm attributes the for-
mation of benzimidaolium salts 1a‐c. The Ru (II)‐NHC
complexes were synthesized through silver‐NHC interme-
diate by the reaction of ligand precursor with silver(I)
oxide to form Ag‐NHC. Further, the Ag‐NHC was treated
with Ru (II) arene precursors and kept for stirring at
room temperature for 6 hr and filtered through celite
plug. Then, addition of pet‐ether to the filtrate leads to
the precipitation of browny Ru (II)‐NHC complexes 2a‐f
in good yield (Scheme 3). The above complexes are solu-
ble in polar solvents like CHCl3, CH2Cl2, CH3OH, DMF,
DMSO and insoluble in non‐polar solvents.
2.13 | General procedure for quinoline
synthesis
1
In the H NMR spectra, a sharp singlet was appeared
Ketones (0.5 mmol), 2‐aminobenzyl alcohol (0.5 mmol),
catalyst 2a (2.26 mg, 0.5 mol%), NaOH (8 mg, 0.2 equiv)
and toluene (2 ml) were charged into a round neck flask
and heated at 105 °C for 8 h. The progress of the reaction
was monitored by TLC. Upon completion, the solvent
was evaporated and the residue was purified by column
chromatography over silica gel (60–120 mesh) with
hexane/ethyl acetate (90:10) mixture as eluent.
at 10–11 ppm due to NCHN proton of 5,6‐
dimethylbenzimidazolium salts 1a‐c which was disap-
peared after the carbene carbon coordination to ruthe-
nium center in the complexes 2a‐f. The 13C{1H} NMR
data strongly revealed the formation of Ru‐Ccarbene bond
and the corresponding signals were observed at 180–
190 ppm as expected for (arene) Ru (NHC) compounds
2a‐f. From the spectral data, it is worth to note that the
carbene ligand coordinated to Ru (II) ion via carbenic
carbon. Furthermore, the HR‐MS spectrometry technique
was used to determine the exact mass of the complexes.
The HR‐MS spectra of complexes 2a‐f displayed peaks
at m/z = 417.0664, [2a, M‐Cl]+, m/z = 553.4167, [2b,
M‐Cl]+, m/z = 541.0975, [2c, M‐Cl]+, m/z = 473.1292,
3 | RESULTS AND DISCUSSION
5,6‐dimethylbenzimidazolin‐2‐ylidene ligands were syn-
thesized as previously described in the literature with
c, 20
slight modification.15b,
The N, N′‐bisalkylation of
SCHEME 3 Synthetic route of NHC
ligands 1a‐c and Ru (II) NHC complexes
2a‐f

6 of 13
BALAMURUGAN ET AL.
[2d, M‐Cl]+, m/z
=
609.2541, [2e, M‐Cl]+ and
m/z = 597.1600, [2f, M‐Cl]+. The [M‐Cl]+ pattern of the
complexes pointed out that the chloro (Cl−) group is
labile in solution phase and easily displaced at different
catalytic reaction conditions.
The molecular structure of the three complexes 2a, 2c
and, 2d are displayed in the Figure 1–3 with selected
bond distances and angles. The summary of X‐ray data
and refinement parameters is given (Table S1 and S2,
see supporting information). The complex 2a was crystal-
lized in “P 1 21/c 1” space group, whereas “A b a 2” space
group for complex 2c and “P 21 21 21” was observed for
2d. The NHC ligands coordinated to Ru (II) ion as
FIGURE 3 ORTEP representation of the complex 2d with 30%
probability level. All hydrogen atoms were omitted for clarity
monodentate manner via neutral carbenic carbon in all
the complexes. The arene is bonded to the metal ion in
η6 fashion as centrosymmetrically and the two chloride
ligands occupy the remaining positions. Hence, a typical
piano‐stool conformation with pseudo octahedral geome-
try has been proposed for all the complexes. Further,
complexes 2c and 2d exhibit similar geometry with slight
changes in bond angles and bond lengths. The structural
data of all the complexes are coincide with the formerly
reported arene ruthenium (II)‐NHC complexes.[21]
After the complete characterization of ruthenium‐
NHC complexes, we were interested to evaluate the cata-
lytic performance of these complexes as catalysts in the α‐
alkylation reaction. To optimize the best catalytic reac-
tion conditions, we consider the formation of benzylated
acetophenone as a benchmark substrate from the reac-
tion of acetophenone with benzyl alcohol in the presence
of Ru (II)‐NHC catalyst 2a with 0.5 mol% (Table 1). Hav-
ing impressed by 98% yield of alkylated product in the
test reaction (Table 1; entry 5), We moved to screen the
catalytic parameters like base, solvent and temperature,
which concluded that the toluene/NaOH at 105 °C were
chosen as the best reaction medium. In addition, when
the reactions were employed in the presence of catalyst
with no base and vice‐versa, there was no appreciable
yield or only trace amount in the alkylated product of
acetophenone (Table 1; entries 14 and 15). Also, when
the reaction was carried out at low temperatures,
(Table 1; entry 10–12) the yield of product was signifi-
cantly decreased. On the whole, the reactivity of the cata-
lyst was found to be effective in the presence of NaOH
when compared to other bases employed in this catalytic
transformation.
FIGURE 1 ORTEP representation of the complex 2a with 30%
probability level. All hydrogen atoms and water molecule were
omitted for clarity
FIGURE 2 ORTEP representation of the complex 2c with 30%
probability level. All hydrogen atoms were omitted for clarity

BALAMURUGAN ET AL.
7 of 13
TABLE 1 Optimization of the reaction conditionsa
wingtips. Also, the catalytic activity of 2c and 2f (Table 2;
entries 15 and 18) showed a sluggishness in the formation
of appreciable yield, this behavior represents the possible
π‐coordination22d of benzyl wingtip to the ruthenium
atom on removal of arene moieties or other ligands under
the catalytic conditions, thus hindering the coordination
and further activation of substrates and intermediates.
Based on the results, it may be concluded that the yield
of alkylation of acetophenone was slightly decreased with
respect to the catalysts 2a‐f with different wingtips and
arene moieties in the following order, ethyl wingtip‐
benzene moiety 2a > ethyl‐wingtip p‐cymene moiety
#
Solvent
T(°C)
110
Base
Yield(%)b
1
t‐amyl alcohol
1,4‐Dioxane
THF
NaOH
NaOH
NaOH
NaOH
NaOH
KOH
73
70
40
55
2
80
70
3
4
Benzene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
80
5
105
105
105
105
105
90
>98
6
90
80
2d
2b
>
>
cyclohexylmethyl wingtip‐benzene moiety
cyclohexylmethyl wingtip‐p‐cymene moiety
7
KOtBu
Cs2CO3
K2CO3
NaOH
NaOH
NaOH
Et3N
2e > benzyl wingtip‐benzene moiety 2c > benzyl
wingtip‐p‐cymene moiety 2 f. Hence, 0.5 mol% of com-
plex 2a with 8 hr reaction time was chosen as the best
optimal reaction condition for the alkylation reaction
and thus used for broad scope of substrate with wide vari-
eties of ketones and primary alcohols.
8
71
9
<32
61
10
11
12
13
14c
15d
50
35
RT
105
105
105
NR
<20
<10
<1
As shown in Table 3, the scope of the α‐alkylation
reaction was investigated with respect to ketones and
alcohols. More interestingly, acetophenone and their
derivatives bearing the electron donating substituents
such as p‐methyl and p‐methoxy enhance the alkylation
process with benzyl alcohol to the desired products 3aa‐
3 ac in 86–92% yields. In case of acetophenone compris-
ing the electron withdrawing substituents, such as p‐
chloro, p‐fluoro and p‐bromo were found to be good cou-
pling partner with benzyl alcohol to the respective
alkylated products 3ad‐3af with the isolated yields of
79–86%. In addition, coupling of p‐nitro acetophenone
with benzyl alcohol afforded only poor yield in the for-
mation of alkylated product 3ag in 37%. Further, the
scope of the reaction was extended to the benzyl alcohol
derivatives. The α‐alkylation of acetophenone with ben-
zyl alcohols bearing methyl and methoxy groups (o‐
and p positions) afforded the corresponding products
3ba‐3bd in 80–91% yields. The present catalytic system
also performed well with methylene ketones, exclusively
for α‐tetralone, which efficiently alkylated with p‐
methoxybenzyl alcohol to the expected product of 3ah
in 89% yield and 1‐indanone smoothly underwent α‐
alkylation with benzyl alcohol and p‐methoxybenzyl
alcohol to the respective 3ai‐3aj with the isolated yield
of 88–90%.
‐
KOH
aConditions: Acetophenone (0.5 mmol), benzyl alcohol (0.5 mmol), catalyst
2a (0.5 mol %), base (0.2 equiv), solvent (2.0 ml) for 24 hr.
bisolated yield.
creaction was performed without base.
dabsence of catalyst, NR – No reaction.
Although suitable base and solvent were established,
the impacts of the nature of wingtip groups and catalyst
loading have to be studied in the alkylation of ketones
to prove the catalytic efficiency of the complexes. For this
purpose, a series of test reactions was conducted using all
the complexes 2a‐f as displayed in the Table 2.
From the results, it was found that the best perfor-
mance was achieved using 0.5 mol% of catalyst loading
in the alkylation process (Table 2). However, the satisfac-
tory yield was attained using 0.3 mol% of catalysts in
24 hr. The moderate yield and highest TON was obtained
by using 0.1 mol% of catalysts loading in longer reaction
time (Table 2; entries 1–6). At this juncture, we also stud-
ied the effect of wingtip group of the complexes 2a‐f in
the α‐alkylation reaction. From these experimental obser-
vations, the complex 2a showed an excellent catalytic per-
formance with 92% yield and outperformed other
complexes in the formation of alkylated product
(Table 2; entries 13–18), indeed the complexes having
smaller wingtip in NHC22a, b along with lability of arene
moiety22c probably influence the hydrogen borrowing
process in α‐alkylation reactions when compared to bulky
Though piperonyl analogues were found in the phar-
maceutically active intermediates,[7] piperonyl derived
α‐alkylated product is less developed in the previous liter-
atures. Hence, we tuned this methodology to explore a
range of piperonyl substituted ketones. Gratifyingly, we
attained the desired ketones (acetophenone, p‐
chloroacetophenone
and
p‐methoxyacetophenone)

8 of 13
BALAMURUGAN ET AL.
TABLE 2 Effect of wingtips and arenes on Ru (II) complexes 2a‐fa
S. No
Wingtips
Amount of cat (mol %)
Time (h)
TONb
Yieldc (%)
1
2a
2b
2c
2d
2e
2f
0.1
0.1
0.1
0.1
0.1
0.1
0.3
0.3
0.3
0.3
0.3
0.3
0.5
0.5
0.5
0.5
0.5
0.5
24
24
24
24
24
24
24
24
24
24
24
24
8
550
430
380
500
390
330
240
213
193
226
203
180
184
154
142
172
146
138
55
43
38
50
39
33
72
64
58
68
61
54
92
77
71
86
73
69
2
3
4
5
6
7
2a
2b
2c
2d
2e
2f
8
9
10
11
12
13
14
15
16
17
18
2a
2b
2c
2d
2e
2f
8
8
8
8
8
aConditions: Acetophenone (0.5 mmol), benzyl alcohol (0.5 mmol), catalysts (0.1–0.5 mol %), NaOH (0.2 equiv) Toluene (2.0 ml) at 105 °C.
bTON: mol of product formed/mol of catalyst used.
cIsolated yield.
having piperonyl moiety 3be‐3bg in 87–93% yield. To our
delight, coupling of 1‐indanone with piperonyl alcohol
gave 3bh in 90% yield.
antimicrobial, anti‐HIV, and for the treatment of neuro-
degenerative diseases)[23] and material chemistry (OLED
complexes and chemo‐sensors)[24] as well as catalysis
(asymmetric synthesis).[25] By the potential behavior of
these quinolines, a large number of attempt has been
made to produce quinolines via classical annulation reac-
tions.[26] Among them, Friedlander synthesis was consid-
ered to be a most suitable method in which the quinoline
product was achieved through the cyclization reaction of
o‐aminobenzaldehydes with ketones. But this method
was highly restricted due to the fact that o‐
aminobenzaldehydes are unstable and easily prone to
self‐condensation.[27] Nevertheless, these methods often
suffer from drawbacks such as difficult availability of
the starting materials, longer reaction time and higher
temperature.
3.1 | One‐pot catalytic synthesis of
quinoline from 2‐aminobenzyl alcohol and
ketones
An excellent catalytic activity of Ru (II)‐NHC complexes
in the alkylation process was further extended to one‐
pot synthesis of quinoline and their derivatives. The utili-
zation of 2‐aminobenzyl alcohol as a more stable starting
material for the annulation via acceptorless
dehydrogenative cyclization processes the being much
attractive towards catalysts seekers.
Generally, quinoline derivatives are known as the
prime candidate of heterocyclic compounds. These scaf-
folds providing a significant contribution in the field of
pharmacology (anti‐tubercular, anticancer, antipsychotic,
Some of the reported complexes of Fe, Ir, Ru and
Co metals[28] were also employed as catalysts in quino-
line synthesis through annulation reactions, but these
catalysts have some drawbacks like high catalyst

BALAMURUGAN ET AL.
9 of 13
TABLE 3 Scope of the reaction in α‐alkylation of ketonesa,b
aConditions: Ketone (0.5 mmol), alcohol (0.5 mmol), catalyst 2a (0.5 mol %), NaOH (0.2 equiv.), Toluene
(2.0 ml) at 105 °C for 8 hr.
bIsolated yield.
loading, harsh reaction condition with moderate yield,
negligible commercialization and their limited utility
in industrial wise.
reaction of acetophenone having electron‐withdrawing
substituent at p‐position afforded the respective product
4ad in 88% yield. Further, the catalytic tolerance was
potentially proved by the reaction of 2‐acetylpyridine, 2‐
acetylthiophene and 2‐acetylfuran with 2‐aminobenzyl
alcohol to the desired products 4ai‐4ak in 82–96% yields.
Also, sterically hindered propiophenone easily coupled
with 2‐aminobenzyl alcohol to the corresponding product
4al in 83% yield. In addition, the 2‐acetyl naphthalene
was successfully converted to a desired product of 4 am
in 90% yield. Also, α‐tetralone underwent cyclization with
amino alcohol to the corresponding 4an in 79% yield.
Furthest, the present catalyst 2a also worked well with
alicyclic ketones such as cyclohexanone, cycloheptanone
and cyclooctanone easily cyclization with 2‐aminobenzyl
alcohol to the desired products 4ae‐4ag in 83–93% yield.
In this connection, we pleased to overcome the afore-
mentioned issues, the present Ru‐NHC catalytic system
was potentially used to cyclize the 2‐aminobenzyl alcohol
with aryl and aliphatic ketones to yield quinolines.
By the impressive result of 4aa in 90% yield using
0.5 mol% 2a in the test reaction as represented in
Table 4. Further, we investigated the substrate scope with
wide range of aromatic, aliphatic ketones and their deriv-
atives under the optimal reaction condition as depicted in
Table 4. Particularly, the acetophenone encompass
electron‐donating substituent at p‐position was rapidly
cyclized with 2‐aminobenzyl alcohol to the corresponding
quinoline products 4aa‐4 ac in 90–92% yields. Also, the

10 of 13
BALAMURUGAN ET AL.
TABLE 4 Scope of the reaction in quinoline synthesisa,b
aConditions: Ketone (0.5 mmol), 2‐aminobenzyl alcohol (0.5 mmol), catalyst 2a (0.5 mol %), NaOH (0.2 equiv), Tol-
uene (2.0 ml) at 105 °C for 8 hr.
bIsolated yield.
SCHEME 4 Plausible catalytic cycle for the α‐alkylation reaction and quinoline synthesis

BALAMURUGAN ET AL.
11 of 13
SCHEME 5 Control experiments
In the case of aliphatic ketone, particularly 2‐pentanone
underwent cyclization with 2‐aminobenzyl alcohol to
form quinoline 4ah in 75% yield.
potential influence of the titled Ru (II) complexes bearing
NHC ligand in facilitating the hydrogen auto transfer
reaction and widens the future opportunities for Ru‐
NHC based methodologies to life saving drug design
and developments.
On the basis of the above experimental observations
and related literatures,[12,29] we proposed a plausible cat-
alytic cycle for the α‐alkylation reaction and quinoline
synthesis using our Ru (II)‐NHC catalyst 2a as displayed
in Scheme 4. In the first step, in the presence of base,
the alcohol was coordinated with Ru (II)‐NHC catalyst I
to form a Ru‐NHC‐alkoxide species II or II’. Next, the
β‐hydride elimination occurs in II or II’ to remove benz-
aldehyde A or 2‐aminobenzaldehyde A' with the forma-
tion of Ru‐hydride[13] species III. Meanwhile, the
aldehyde A or A' reacts with ketone in the presence of
base to form α, β‐unsaturated ketone intermediate B or
B′. Further, B was effectively reduced by Ru‐hydride
(borrowing hydrogen) species to furnish α‐alkylated prod-
uct 3aa and reproduce the catalyst. Moreover, the B′
underwent dehydrative cyclization pathway and affords
quinoline 4aa with the removal of water in open air
condition.19b, f
ACKNOWLEDGMENTS
The authors thank the Council of Scientific & Industrial
Research (CSIR) for financial support (Scheme No:
02(0142)/13/EMR ‐ II) and for Senior Research Fellow-
ship to G.B. We thank UGC‐SAP and DST‐India (FIST
programme) for the use of Bruker 400 MHz NMR spectral
facilities and extend my thanks to DST‐FIST (II) Funded‐
India for the use of HRMS studies at the School of Chem-
istry, Bharathidasan University and also thank Indo‐
French (Scheme No: IFC/5005‐1/2013/1156), India for
the utilizing of GC–MS to our research work.
ORCID
Rengan Ramesh http://orcid.org/0000-0001-8358-9583
3.2 | Control experiment
REFERENCES
The α‐alkylation reaction between ketone and alcohol
proceeds through the chalcone intermediate, which was
well established by several research groups.[12] In our
case, the intermediate has been obtained by the reaction
of ketone and alcohol under similar catalytic condition
after 2 hr (Scheme 5). Further, the formation of interme-
diate was evidenced by GC–MS with the conversion of
71% of a desired chalcone (S26, see supporting informa-
tion) and it was also observed that no conversion was tak-
ing place in the absence of catalyst.
[1] M. B. Smith, J. March, March's Advanced Organic Chemistry,
Wiley‐Interscience, New York 2001 499.
[2] a) G. Guillena, D. J. Ramon, M. Yus, Angew. Chem. Int. Ed.
2007, 46, 2358. b) M. H. S. A. Hamid, P. A. Slatford, J. M. J. Wil-
liams, Adv. Synth. Catal. 2007, 349, 1555. c) G. E. Dobereiner,
R. H. Crabtree, Chem. Rev. 2010, 110, 681. d) G. Guillena, D.
J. Ramon, M. Yus, Chem. Rev. 2010, 110, 1611. e) S. Bahn, S.
Imm, L. Neubert, M. Zhang, H. Neumann, M. Beller,
ChemCatChem 2011, 3, 1853. f) Q. Yang, Q. Wang, Z. Yu,
Chem. Soc. Rev. 2015, 44, 2305.
[3] a) F. A. Carey, R. J. Sundberg (Eds), Advanced Organic Chem-
istry Part B: Reactions and Synthesis, 5th ed., Springer, New
York 2007 1. b) J. Otera (Ed), Modern Carbonyl Chemistry,
Wiley‐VCH, Weinheim 2000. c) D. Caine, in Comprehensive
Organic Chemistry, (Eds: B. M. Trost, I. Fleming, G. Pattenden)
Vol. 3, Pergamon, Oxford 1991 1. d) M. T. Reetz, Angew. Chem.
Int. Ed. Engl. 1982, 21, 96. Angew. Chem. 1982, 94, 97 e) D.
Caine, in Comprehensive Organic Chemistry, (Eds: B. M. Trost,
I. Fleming, G. Pattenden) Vol. 3, Pergamon, Oxford 1991 1.
4 | CONCLUSIONS
To provide a sustainable synthetic route to α‐alkylated
ketones and bioactive quinolines scaffolds, the titled com-
plexes were synthesized by operationally‐simple proce-
dure. The catalytic effectiveness of the titled complexes
were well explored for α‐alkylation of a wide range of
ketones with primary alcohols via hydrogen borrowing
technique in good yields with 0.5 mol% of catalyst with-
out of additives. Quinoline synthesis was accomplished
in an excellent yield under similar catalytic condition.
Remarkably, the present investigation symbolizing the
[4] a) M. H. G. Prechtl, K. Wobser, N. Theyssen, Y. Ben‐David, D.
Milstein, W. Leitner, Catal. Sci. Technol. 2012, 2, 2039. b) B.
Gnanaprakasam, E. Balaraman, C. Gunanathan, D. Milstein,
J. Polym. Sci., Part A: Polym. Chem. 2012, 50, 1755. c) D.
Srimani, E. Balaraman, B. Gnanaprakasam, Y. Ben‐David, D.
Milstein, Adv. Synth. Catal. 2012, 354, 2403. d) A. Tillack, D.

12 of 13
BALAMURUGAN ET AL.
Hollmann, D. Michalik, M. Beller, Tetrahedron Lett. 2006, 47,
2012, 14, 18. d) F.‐X. Yan, M. Zhang, X.‐T. Wang, F. Xie, M.‐M.
Chen, H. Jiang, Tetrahedron 2014, 70, 1193.
8881. e) D. Hollmann, A. Tillack, D. Michalik, R. Jackstell,
M. Beller, Chem. – Asian J. 2007, 2, 403. f) A. Tillack, D.
Hollmann, K. Mevius, D. Michalik, S. Bähn, M. Beller, Eur. J.
Org. Chem. 2008, 2008, 4745. g) M. Zhang, S. Imm, S. Bähn,
H. Neumann, M. Beller, Angew. Chem. Int. Ed. 2011, 50,
11197. h) M. H. S. A. Hamid, J. M. J. Williams, Chem.
Commun. 2007, 725. i) M. H. S. A. Hamid, J. M. J. Williams,
Tetrahedron Lett. 2007, 48, 8263. j) M. H. S. A. Hamid, C. L.
Allen, G. W. Lamb, A. C. Maxwell, H. C. Maytum, A. J. A. Wat-
son, J. M. J. Williams, J. Am. Chem. Soc. 2009, 131, 1766. k) A.
J. A. Watson, A. C. Maxwell, J. M. J. Williams, J. Org. Chem.
2011, 76, 2328. l) R. N. Monrad, R. Madsen, Org. Biomol. Chem.
2011, 9, 610. m) K. Yamaguchi, J. He, T. Oishi, N. Mizuno,
Chem. – Eur. J. 2010, 16, 7199. n) S. Agrawal, M. Lenormand,
B. Martin‐ Matute, Org. Lett. 2012, 14, 1456. o) F. E. Fernández,
M. C. Puerta, P. Valerga, Organometallics 2012, 31, 6868. p) A.
B. Enyong, B. Moasser, J. Org. Chem. 2014, 79, 7553. q) E.
Balaraman, D. Srimani, Y. Diskin‐Posner, D. Milstein, Catal.
Lett. 2015, 145, 139.
[10] a) M.‐H. S. A. Hamid, P. A. Slatford, J. M. J. Williamsa, Adv.
Synth. Catal. 2007, 349, 1555. b) A. Corma, J. Navas, M. J.
Sabater, Chem. Rev. 2018, 118, 1410. c) T. D. Nixon, M. K.
Whittlesey, J. M. J. Williams, Dalton Trans. 2009, 753. d) S.
Kerdphon, X. Quan, V. S. Parihar, P. G. Andersson, J. Org.
Chem. 2015, 80, 11529.
[11] W. Chang, X. Gong, S. Wang, L.‐P. Xiao, G. Song, Org. Biomol.
Chem. 2017, 15, 3466.
[12] C. Schlepphorst, B. Maji, F. Glorius, ACS Catal. 2016, 6, 4184.
[13] X.‐N. Cao, X.‐M. Wan, F.‐L. Yang, K. Li, X.‐Q. Hao, T. Shao, X.
Zhu, M.‐P. Song, J. Org. Chem. 2018, 83, 3657.
[14] a) X. Xie, H. V. Huynh, ACS Catal. 2015, 5, 4143. b) M.
Kaloğlu, N. Gürbüz, D. Sémeril, İ. Özdemir, Eur. J. Inorg.
Chem. 2018, 2018, 1236. c) Z. Şahin, N. Gürbüz, İ. Özdemir,
O. Şahin, O. BüyükgüngÖr, M. Achard, C. Bruneau, Organo-
metallics 2015, 34, 2296. d) S. Horn, C. Gandolfi, M. Albrecht,
Eur. J. Inorg. Chem. 2011, 2863. e) M. Nussbaum, O. Schuster,
M. Albrecht, Chem. – Eur. J. 2013, 19, 17517. f) M. Albrecht,
Chem. Rev. 2010, 110, 576. g) K. F. Donnelly, R. Lalrempuia,
H. Müller‐Bunz, M. Albrecht, Organometallics 2012, 31, 8414.
[5] a) A. Corma, J. Navas, M. J. Sabater, Chem. Rev. 2018, 118,
1410. b) K. O. Marichev, J. M. Takacs, ACS Catal. 2016, 6,
2205. c) A. B. Enyong, B. Moasser, J. Org. Chem. 2014, 79, 7553.
[15] a) S. Patil, A. Deally, B. Gleeson, H. Müller‐Bunz, F. Paradisi,
M. Tacke, Metallomics 2011, 3, 74. b) S. Gülcemal, A. G.
Gökçeb, B. Çetinkaya, Dalton Trans. 2013, 42, 7305. c) S.
Gülcemal, A. G. GÖkçe, B. Çetinkaya, Inorg. Chem. 2013, 52,
10601.
[6] a) S. J. Pridmore, J. M. J. Williams, Tetrahedron Lett. 2008, 49,
7413. b) G. W. Lamb, A. J. A. Watson, K. E. Jolley, A. C.
Maxwell, J. M. J. Williams, Tetrahedron Lett. 2009, 50, 3374.
c) M. Haniti, S. A. Hamid, C. Liana Allen, G. W. Lamb, A. C.
Maxwell, H. C. Maytum, A. J. A. Watson, J. M. J. Williams,
J. Am. Chem. Soc. 2009, 131, 1766. d) M. L. Buil, A. Miguel, J.
Esteruelas, S. Herrero, I. M. Izquierdo, M. Y. Pastor, ACS Catal.
2013, 3, 2072. e) X. Yu, R. Zhao, H. Wan, Y. Yang, D. Wang,
Tetrahedron Lett. 2016, 57, 4588. f) A. E. Putra, Y. Oe, T. Ohta,
Tetrahedron Lett. 2017, 58, 1098.
[16] S. Gülcemal, A. Labande, J. C. Daran, B. Çetinkaya, R. Poli,
Eur. J. Inorg. Chem. 2009, 1806.
[17] S. Gülcemal, J. C. Daran, B. Çetinkaya, Inorg. Chim. Acta 2011,
365, 264.
[18] a) F. E. Hahn, L. Wittenbecher, D. Le Van, R. Fröhlich, Angew.
Chem. Int. Ed. 2000, 39, 541. b) F. E. Hahn, L. Wittenbecher, R.
Boese, D. Bläser, Chem. – Eur. J. 1999, 5, 1931.
[7] J. Leonard, A. John Blacker, S. P. Marsden, M. F. Jones, K. R.
Mulholland, R. Newton, Org. Process Res. Dev. 2015, 19, 1400.
[19] a) E. Sindhuja, R. Ramesh, Y. Liu, Dalton Trans. 2012, 41, 5351.
b) E. Sindhuja, R. Ramesh, S. Balaji, Y. Liu, Organometallics
2014, 33, 4269. c) E. Sindhuja, R. Ramesh, Tetrahedron Lett.
2014, 55, 5504. d) S. Muthumari, R. Ramesh, RSC Adv. 2016,
6, 52101. e) S. Saranya, R. Ramesh, J. G. Małecki, Eur. J. Org.
Chem. 2017, 2017, 6726. f) T. S. Manikandan, R. Ramesh, N.
Shivalingegowda, L. N. Krishnappagowda, ChemistrySelect
2018, 3, 1561. g) T. S. Manikandan, R. Ramesh, D. Semeril,
RSC Adv. 2016, 6, 97107.
[8] G. Chelucci, Coord. Chem. Rev. 2017, 331, – and the references
therein. a) Y. Obora, Top. Curr. Chem. 2016, 374, 11. b) D.
Wang, K. Zhao, P. Ma, C. Xu, Y. Ding, Tetrahedron Lett.
2014, 55, 7233. c) S. Ogawa, Y. Obora, Chem. Commun. 2014,
50, 2491. d) C. Xu, X.‐M. Dong, Z.‐Q. Wang, X.‐Q. Hao, Z. Li,
L.‐M. Duan, B.‐M. Ji, M.‐P. Song, J. Organomet. Chem. 2012,
700, 214. e) K. Taguchi, H. Nakagawa, T. Hirabayashi, S.
Sakaguchi, Y. Ishii, J. Am. Chem. Soc. 2004, 126, 72. f) Y. M.
A. Yamada, Y. Uozumi, Org. Lett. 2006, 8, 1375. g) M. S. Kwon,
N. Kim, S. H. Seo, I. S. Park, R. K. Cheedrala, J. Park, Angew.
Chem. Int. Ed. 2005, 44, 6913. h) C. S. Cho, J. Mol. Catal. A
2005, 240, 55. i) X. Yu, Q. Y. Wang, Q. J. Wu, D. W. Wang,
Russ. J. Gen. Chem. 2016, 86, 178. j) S. Elangovan, J.‐B. Sortais,
M. Beller, C. Darcel, Angew. Chem. Int. Ed. 2015, 54, 14483. k)
G. Zhang, J. Wu, H. Zeng, S. Zhang, Z. Yin, S. Zheng, Org. Lett.
2017, 19, 1080. l) N. Deibl, R. Kempe, J. Am. Chem. Soc. 2016,
138, 10786. m) S. Liao, K. Yu, Q. Li, H. Tian, Z. Zhang, X.
Yu, Q. Xu, Org. Biomol. Chem. 2012, 10, 2973.
[20] L. Oehninger, M. Stefanopoulou, H. Alborzinia, J. Schur, S.
Ludewig, K. Namikawa, A. Muñoz‐Castro, R. W. Köster, K.
Baumann, S. Wölfl, W. S. Sheldrickb, I. Ott, Dalton Trans.
2013, 42, 1657.
[21] S. P. Shan, X. Xiaoke, B. Gnanaprakasam, T. T. Dang, B.
Ramalingam, H. V. Huynh, A. M. Seayad, RSC Adv. 2015, 5,
4434.
[22] a) F. E. Fernández, M. Carmen Puerta, P. Valerga, Organome-
tallics 2012, 31, 6868. b) G. Balamurugan, R. Ramesh, J. G.
Malecki, ChemistrySelect 2017, 2, 10603. c) J. DePasquale, M.
Kumar, M. Zeller, E. T. Papish, Organometallics 2013, 32, 966.
d) N. Gürbüz, S. Yasar, E. Ö. Özcan, Đ. Özdemir, B. Çetinkaya,
Eur. J. Inorg. Chem. 2010, 3051.
[9] References for Ru (II) precusors a) C. S. Cho, B. T. Kim, T.‐J.
Kim, S. C. Shim, Tetrahedron Lett. 2002, 43, 7987. b) R. Martí-
nez, G. J. Brand, D. J. Ramón, M. Yus, Tetrahedron Lett.
2005, 46, 3683. c) T. Kuwahara, T. Fukuyama, I. Ryu, Org. Lett.

BALAMURUGAN ET AL.
13 of 13
[23] a) R. S. Keri, S. A. Patil, Biomed. Pharmacother. 2014, 68, 1161.
b) V. R. Solomon, H. Lee, Curr. Med. Chem. 2011, 18, 1488. c) S.
Vlahopoulos, E. Critselis, I. F. Voutsas, S. A. Perez, M.
Moschovi, C. N. Baxevanis, G. P. Chrousos, Curr. Drug Targets
2014, 15, 843. d) J. Szmuszkovicz, W. H. Darlington, P. F. Von
Voigtlander, Patent WO 8804292A1, 1988. Chem. Abstr. 1988,
110, 75335 e) R. R. Bahuguna, B. C. Joshi, H. N. Mangal,
J. Indian Chem. Soc. 1992, 69, 401. f) K. R. Fandrick, W. Li,
Y. Zhang, W. Tang, J. Gao, S. Rodriguez, N. D. Patel, D. C.
Reeves, J.‐P. Wu, S. Sanyal, N. Gonnella, B. Qu, N. Haddad,
J. C. Lorenz, K. Sidhu, J. Wang, S. Ma, N. Grinberg, H. Lee,
Y. Tsantrizos, M.‐A. Poupart, C. A. Busacca, N. K. Yee, B. Z.
Lu, C. H. Senanayake, Angew. Chem. Int. Ed. 2015, 54, 7144.
g) S. Bongarzone, M. L. Bolognesi, Expert Opin. Drug Discovery
2011, 6, 251.
Martinez, G. J. Brand, D. J. Ramon, M. Yus, Tetrahedron Lett.
2005, 46, 3683. e) R. Martinez, D. J. Ramon, M. Yus, Eur. J.
Org. Chem. 2007, 2007, 1599. f) H. V. Mierde, P. V. D. Voort,
D. D. Vos, F. Verpoort, Eur. J. Org. Chem. 2008, 1625. g) C. S.
Cho, W. X. Ren, J. Organomet. Chem. 2007, 692, 4182. h) B.
W. J. Chen, L. L. Chng, J. Yang, Y. Wei, J. Yang, J. Y. Ying,
ChemCatChem 2013, 5, 277. i) K. Taguchi, S. Sakaguchi, Y.
Ishii, Tetrahedron Lett. 2005, 46, 4539. j) C. S. Cho, W. X.
Ren, S. C. Shim, Tetrahedron Lett. 2006, 47, 6781. k) C. S.
Cho, W. X. Ren, N. S. Yoon, J. Mol. Catal. A: Chem. 2009,
299, 117.
[29] a) F. Huang, Z. Liu, Z. Yu, Angew. Chem. Int. Ed. 2016, 55, 862.
b) S. Elangovan, J.‐B. Sortais, M. Beller, C. Darcel, Angew.
Chem. Int. Ed. 2015, 54, 14483.
[24] a) J. I. Kim, I.‐S. Shin, H. Kim, J.‐K. Lee, J. Am. Chem. Soc.
2005, 127, 1614. b) H. Tong, L. Wang, X. Jing, F. Wang, Macro-
molecules 2003, 36, 2584. c) G. E. Tumambac, C. M.
Rosencrance, C. Wolf, Tetrahedron 2004, 60, 11293.
SUPPORTING INFORMATION
Additional supporting information may be found online
in the Supporting Information section at the end of the
article.
[25] a) J. He, R. Takise, H. Y. Fu, J. Q. Yu, J. Am. Chem. Soc. 2015,
137, 4618. b) Z. C. Jin, X. Wang, H. C. Huang, X. M. Liang, J. X.
Ye, Org. Lett. 2011, 13, 564. c) W. J. Nodes, D. R. Nutt, A. M.
Chippindale, A. J. A. Cobb, J. Am. Chem. Soc. 2009, 131, 16016.
How to cite this article: Balamurugan G, Balaji
S, Ramesh R, Bhuvanesh NSP. Synthesis and
Structures of Arene Ruthenium (II)–NHC
Complexes: Efficient Catalytic α‐alkylation of
ketones via Hydrogen Auto Transfer Reaction.
Appl Organometal Chem. 2018;e4696. https://doi.
org/10.1002/aoc.4696
[26] G. Jones, in Comprehensive Heterocyclic Chemistry, (Eds: A. R.
Katritzky, C. W. Rees) Vol. 2, Pergamon, New York 1984 395.
[27] E. J. Perez‐Mayoral, A. Samadi, M. C. Carreiras, E. Soriano,
Chem. Rev. 2009, 109, 2652.
[28] a) C. S. Cho, B. T. Kim, T. J. Kim, S. C. Shim, Chem. Commun.
2001, 2576. b) C. S. Cho, B. T. Kim, H. J. Choi, T. J. Kim, S. C.
Shim, Tetrahedron 2003, 59, 7997. c) K. Motokura, T. Mizugaki,
K. Ebitani, K. Kaneda, Tetrahedron Lett. 2004, 45, 6029. d) R.