Ruthenium(II) complexes containing phosphino hydrazone/thiosemicarbazone ligand: An efficient catalyst for regioselective N-alkylation of amine via borrowing hydrogen methodology

Article abstract of DOI:10.1016/j.ica.2018.03.007

In the aspect of more effective ruthenium based catalyst design, three new ruthenium(II) phosphino-hydrazone/thiosemicarbazone complexes (1–3) have been synthesized by the reactions of cis-[RuCl₂(dmso)₄] or [RuHCl(CO)(AsPh₃)₃] with deprotonated 2-(2-(diphenylphosphino)benzylidene)-2-thiophenecarboxylic acid hydrazone (PNO-Thy) or 2-(2-(diphenylphosphino)benzylidene)-4-phenyl-3-thiosemicarbazone (PNS-Ph). The structures of the complexes (2 and 3) were established by X-ray crystallography and spectroscopic methods including elemental analysis, FT-IR and NMR (¹H, ¹³C & ³¹P). Single crystal XRD upshots of complexes (2 and 3) revealed a distorted octahedral geometry around the ruthenium ion with hydrazone/thiosemicarbazone acts as a monoanionic tridentate PNO/PNS donor fashion. The catalytic study of complexes 1–3 towards regioselective N-alkylation reactions of amines was completed, showing that all catalysts are active toward catalytic transformations. Notably, complex 3 was found to be very efficient catalysts toward N-alkylation of a wide range of heterocyclic amines with alcohols. This catalysis provides a clean, convenient and practical route for the direct N-alkyl amine synthesis.

Full text of DOI:10.1016/j.ica.2018.03.007

Accepted Manuscript
Research paper
Ruthenium(II) complexes containing phosphino hydrazone/thiosemicarbazone
ligand: An efficient catalyst for regiselective N-alkylation of amine via borrow-
ing hydrogen methodology
R. Ramachandran, G. Prakash, P. Viswanathamurthi, J.G. Malecki
PII:
S0020-1693(17)31882-0
https://doi.org/10.1016/j.ica.2018.03.007
ICA 18152
DOI:
Reference:
Inorganica Chimica Acta
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Accepted Date:
12 December 2017
28 February 2018
8 March 2018
Please cite this article as: R. Ramachandran, G. Prakash, P. Viswanathamurthi, J.G. Malecki, Ruthenium(II)
complexes containing phosphino hydrazone/thiosemicarbazone ligand: An efficient catalyst for regiselective N-
alkylation of amine via borrowing hydrogen methodology, Inorganica Chimica Acta (2018), doi: https://doi.org/
10.1016/j.ica.2018.03.007
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Ruthenium(II) complexes containing phosphino hydrazone/thiosemicarbazone
ligand: An efficient catalyst for regiselective N-alkylation of amine via
borrowing hydrogen methodology
R. Ramachandrana, 1, G. Prakasha, 1, P. Viswanathamurthia, *, J. G. Maleckib
aDepartment of Chemistry, Periyar University, Salem-636 011, India.
bDepartment of Crystallography, Silesian University, Szkolna 9, 40-006 Katowice, Poland.
*To whom correspondence should be addressed, E-mail: viswanathamurthi@gmail.com
Fax: +91 427 2345124
1Present address: Department of Chemistry, Indian Institute of Technology, Indore- 453 552,
India

ABSTRACT
In the aspect of more effective ruthenium based catalyst design, three new ruthenium(II)
phosphino-hydrazone/thiosemicarbazone complexes (1-3) have been synthesized by the reactions
of cis-[RuCl2(dmso)4] or [RuHCl(CO)(AsPh3)3] with deprotonated 2-(2-
(diphenylphosphino)benzylidene)-2-thiophenecarboxylic acid hydrazone (PNO-Thy) or 2-(2-
(diphenylphosphino)benzylidene)-4-phenyl-3-thiosemicarbazone (PNS-Ph). The structures of the
complexes (2 and 3) were established by X-ray crystallography and spectroscopic methods
13
31
including elemental analysis, FT-IR and NMR (1H, C & P). Single crystal XRD upshots of
complexes (2 and 3) revealed a distorted octahedral geometry around the ruthenium ion with
hydrazone/thiosemicarbazone acts as a monoanionic tridentate PNO/PNS donor fashion. The
catalytic study of complexes 1-3 towards regioselective N-alkylation reactions of amines was
completed, showing that all catalysts are active toward catalytic transformations. Notably,
complex 3 was found to be very efficient catalysts toward N-alkylation of a wide range of
heterocyclic amines with alcohols. This catalysis provides a clean, convenient and practical route
for the direct N-alkyl amine synthesis.
Key words: Thiosemicarbazone, Hydrazone ligands, Ruthenium complexes, N-alkylation

1.
Introduction
Hydrazones and thiosemicarbazones are versatile ligands of considerable attention with respect
to their variable coordination behavior and promising biological [1] and catalytic properties [2].
To tune the catalytic activity or increase the activity [3], the hydrazones/thiosemicarbazones
framework is functionalized by different group and studied in a number of cases [4]. Phosphino-
hydrazones/thiosemicarbazones [5] occupied prominent position among the several
functionalized thiosemicarbazone derivatives [6]. With the simultaneous presence of soft and
hard donors, the phosphino-functionalized ligands exhibit various coordination modes: PNS-
tridentate [7-9], P-S bidentate [10] and P-S bridge in binuclear compounds as well as in
oligomers [11]. This makes structural studies more interesting, which are the rational base for
structure-activity relationships. This variable mode of binding of phosphino-thiosemicarbazone
has encouraged us to explore its coordination chemistry further although a large number of
reports are available on the chemistry and biological activity of metal complexes containing
thiosemicarbazonates [12-15].
The interest in coordination complexes of ruthenium stems from their versatile electron-
transfer and energy-transfer properties [16]. Ruthenium offers a wide range of oxidation state
and the reactivity’s of the ruthenium complexes depend on the stability and inter convert ability
of these oxidation states which in turn, depends on the nature of the ligands bound to the metal.
Ruthenium complexes have also proved to be useful catalysts in many reactions such as
oxidation, hydrogenation, carboxylation and hydroformylation [17]. Phosphine based ligands
have found widespread application not only in coordination chemistry but also in industrial
applications of homogeneous catalysis. Particularly, ruthenium phosphine complexes are known
to possess catalytic properties which are of great value in organic synthesis [18].
The catalytic construction of C−N bonds via borrowing hydrogen methodology, have
recently received much attention since nitrogen functionalities occur in various compounds of
synthetic and pharmaceutical significance as well as in important biologically active molecules
[19-23]. In contrast with other transition-metal-catalyzed methodologies, e.g., amination of
organohalides (Buchwald-Hartwig amination) [24], reductive amination of carbonyl compounds
[25], hydroamination [26] and hydroaminomethylation [27] of carbon-carbon unsaturated
compounds, etc., [28] the N-alkylation of amines with alcohols, produced water as the sole by-

product, may serve as a relatively green and environmentally benign alternative [29]. Moreover
the use of alcohols as the alkylating agent is direct and simple as the alcohols are readily
available, highly stable, low in toxicity, easily stored and handled, low in cost, and relatively
high in atom efficiency. While both heterogeneous and homogeneous catalysts have been known
to promote the reaction [30-34], ruthenium [31-33] and iridium [34] complexes have constituted
a vast majority of the homogeneous catalysts because of their relatively high catalytic
performance with high product selectivity [35, 36]. Several iridium and ruthenium catalytic
systems bearing phosphine ligands [37-41] have been reported to complete the N-alkylation of
amines with alcohols by means of good yields and selectivity. Some transition-metal-free
systems have been reported for the N-alkylation of amines with alcohols which worked under
mild conditions for shorter reaction times and also provide good yields [42]. However, certain
demerits of these systems such as availability, requirement of additives, poor selectivity,
economy, TON etc can be overcome or improved by transition metal catalysts as alternatives.
During our ongoing exploration of highly active transition metal complex catalysts for
homogeneous catalysis, we have disclosed that pyridine carboxamide, thiosemicarbazone and
hydrazones with ONS, NNS, PNS and O2N2 functionalities [43] in Ru(II) and CuI complex
catalyst can show a remarkable acceleration effect on the N-alkylation amines. Based on the
above facts, the present work deals with synthesis, structures and catalytic activity of new
ruthenium(II) complexes of multidentate phosphino-hydrazone/thiosemicarbazones. The new
complexes have been characterized by elemental analysis, spectroscopic and X-ray
crystallography studies. In addition, the complexes have also been subjected to catalytic activity.
2. Experimental
2.1 Materials and methods
All reagents were purchased from Aldrich as high-purity products and generally used as
received; all solvents were used as received as technical-grade solvents. Unless otherwise noted,
all reactions were performed under an atmosphere of air. Thin-layer chromatography (TLC) was
carried out on Merck 1.05554 aluminum sheets precoated with silica gel 60 F254 and the spots
were visualized with UV light at 254 nm or under iodine. Column chromatography purifications
were performed by using Merck silica gel 60 (0.063-0.200 mm). Elemental analysis (C, H, N, S)

were done on a Vario EL III Elemental analyzer. Infrared spectra of the ligands and the metal
complexes were recorded as KBr discs in the range of 4000−400 cm−1 using a Nicolet Avatar
1
13
31
model FT-IR spectrophotometer. H (300 and 400 MHz), C (100 MHz) and P NMR (162
MHz) spectra were taken in DMSO-d6 or CDCl3 at room temperature with a Bruker AV400
instrument with chemical shifts relative to tetramethylsilane (1H, 13C) and o-phosphoric acid
(31P). Mass spectra were drawn on a LC−MS Q−ToF Micro Analyzer (Shimadzu), using
electrospray ionization (ESI) mode. The melting points were checked with a Lab India melting
point apparatus.
Crystals of 2 and 3 were mounted on glass fibers and used for data collection. Crystal
data were collected at 295 K using a Gemini A Ultra Oxford Diffraction automatic
diffractometer. Graphite monochromated Mo-Kα radiation (λ = 0.71073 Å) was used throughout.
The absorption corrections were performed by the multi-scan method. Corrections were made for
Lorentz and polarization effects. The structures were solved by direct methods using the program
SHELXS [44]. Refinement and all further calculations were carried out using SHELXL. The H
atoms were included in calculated positions and treated as riding atoms using the SHELXL
default parameters. The non-hydrogen atoms were refined anisotropically, using weighted full-
matrix least squares on F2. In the solid state, a disorder is observed within the two different
enantiomeric forms in such a manner that only the carbonyl group and the chlorine atom share
the ligand positions mutually. The reported method was used for the synthesis of
[RuHClCO(AsPh3)3] [45] and cis-[RuCl2(dmso)4] [46].
2.2 Synthesis of 2-(2-(diphenylphosphino)benzylidene)-2-thiophenecarboxylic acid hydrazone
(PNO-THy) ligand
To a solution of 2-(diphenylphosphino)benzaldehyde (0.290 g, 1 mmol) and 2-thiophene
carboxylic acid hydrazide (0.126 g, 1 mmol) in ethanol (20 mL) were added 2−3 drops of glacial
acetic acid. The resulting solution was heated under reflux over a 3 h period, and then
concentrated to ca. 3 mL. The white crystalline precipitate was filtered off, washed with diethyl
ether (2 x 5 mL), and dried under vacuo. Yield: 87% (0.36 g). Mp: 197−199 °C. Anal. Calcd for
C24H19N2OPS: C, 69.55; H, 4.62; N, 6.76; S, 7.74. Found: C, 69.67; H, 4.58; N, 6.86; S, 7.69. IR
1
(KBr disks, cm−1): 3195 (m, νNH); 1685 (s, νC=O); 1583 + 1474 (s, νC=N + νC−N). H NMR (400
MHz, DMSO-d6, ppm): 6.83−7.50 (m, 14H, Ar H), 7.57 (t, 1H, J = 6.24, Hz Ar H), 8.05 (s, 1H,

Ar H), 8.15 (s, 1H, Ar H), 8.85 (d, IH, J = 3.6 Hz, −CH=N ), 9.13 (s, 1H, Ar H), 11.98 (s, IH,
13
−NH). C NMR (100 MHz, DMSO-d6, ppm): 125.78 (Ar C), 128.91 (Ar C), 129.15 (Ar C),
129.47 (Ar C), 130.07 (Ar C), 133.30 (Ar C), 133.49 (Ar C), 134.12 (Ar C), 135.62 (Ar C),
138.25 (Ar C), 149.52 (−CH=N), 158.12 (C=O). 31P NMR (162 MHz, DMSO-d6, ppm): −17.14.
2.3 Synthesis of 2-(2-(diphenylphosphino)benzylidene)-4-phenyl-3-thiosemicarbazone (PNS-Ph)
ligand
To a solution of 2-(diphenylphosphino)benzaldehyde (0.290 g, 1 mmol) and 4-phenyl-3-
thiosemicarbazide (0.167 g, 1 mmol) in ethanol (20 mL) were added 2−3 drops of glacial acetic
acid. The pale yellow solution was heated under reflux over a 2 h period, and then concentrated
to dryness. The resulting yellow oil was treated with diethyl ether (2 х 5 mL). The pale yellow
precipitate was filtered off, washed with diethyl ether (10 mL) and dried under vacuo. Mp: 198
°C. Anal. Calcd for C20H18N3P2S: C, 60.91; H, 4.60; N, 10.65; S, 8.13%. Found: C, 60.99; H,
4.62; N, 10.60; S, 8.16%. IR (KBr disks, cm−1): 3303 (m, νNH); 1594 + 1546 (s, νC=N + νC−N); 744
(s, νC=S). 1H NMR (400 MHz, DMSO-d6, ppm): 6.80 (t, 1H, J = 4.8, Ar H), 7.16−7.45 (m, 12H,
Ar H), 7.52 (d, 2H, J = 7.6 Hz, Ar H), 8.31−8.34 (m, 1H, −NHterminal), 8.79 (d, 1H, J = 4.4 Hz,
13
−CH=N), 11.94 (s, 1H, −NHhydrazinic). C NMR (100 MHz, DMSO-d6, ppm): 125.26 (Ar C),
125.55 (Ar C), 127.44 (Ar C), 128.01 (Ar C), 128.78 (Ar C), 128.85 (Ar C), 129.01 (Ar C),
129.12 (Ar C), 129.87 (Ar C), 132.94 (Ar C), 133.36 (Ar C), 133.56 (Ar C), 135.60 (Ar C),
135.70 (Ar C), 136.05 (Ar C), 136.24 (Ar C), 137.24 (Ar C), 137.43 (Ar C), 138.82 (Ar C),
141.07 (−CH=N), 175.81 (C=S). 31P NMR (162 MHz, DMSO-d6, ppm): −11.12.
2.4 Synthesis of [Ru(PNO-THy)2] (1)
A suspension of [RuCl2(dmso)4] (0.2 g, 0.44 mmol) in CH2Cl2 (20 mL) was treated with
PNO-THy (0.364 g, 0.88 mmol) in ethanol (30 mL) and the mixture was gently refluxed for 6 h.
During this time the color changed to dark red. The solvent was removed on a rotary evaporator.
The residue was then chromatographed on alumina oxide with ethyl acetate/petroleum ether. A
red band was eluted with 6:4 ethyl acetate/ petroleum ether mixture and it was identified as 1
(yield 78%). Mp: 259 °C. Anal. Calcd for C48H36N4O2P2RuS2: C, 62.13; H, 3.91; N, 6.04; S,
6.91%. Found: C, 62.31; H, 3.98; N, 6.24; S, 6.98%. IR (KBr disks, cm−1): 3441, 3204 (m, νNH);
1572 + 1481 (s, νC=N + νC−N), 1276 (s, νC-O). 1H NMR (400 MHz, DMSO-d6, ppm): 6.57 (m, 4H,

J = 7.2 Hz, Ar H), 6.70 (t, 2H, J = 8.8 Hz, Ar H), 6.84 (t, 6H, J = 7.2 Hz, Ar H), 7.75−7.02 (m,
13
18H, Ar H), 7.86 (t, 2H, J = 7.2 Hz, Ar H), 8.46 (d, 2H, J = 8.3 Hz, −CH=N). C NMR (100
MHz, DMSO-d6, ppm): 128.00 (Ar C), 128.10 (Ar C), 128.41 (Ar C), 128.64 (Ar C), 129.06 (Ar
C), 129.89 (Ar C), 130.32 (Ar C), 130.48 (Ar C), 131.03 (Ar C), 131.29 (Ar C), 131.38 (Ar C),
131.68 (Ar C), 131.79 (Ar C), 132.80 (Ar C), 132.91 (Ar C), 133.12 (Ar C), 133.54 (Ar C),
133.79 (Ar C), 133.90 (Ar C), 134.00 (Ar C), 138.91 (C=N), 161.80 (C−O). 31P NMR (162
MHz, DMSO-d6, ppm): 29.12 (s, PPh2). ESI-MS: m/z = 927.81 [M]+.
2.5 Synthesis of [Ru(PNS-Ph)2] (2)
A suspension of [RuCl2(dmso)4] (0.2 g, 0.44 mmol) in CH2Cl2 (20 mL) was treated with
PNS-Ph (0.386 g, 0.88 mmol) in ethanol (30 mL) and the mixture was gently refluxed for 6 h.
During this time the colour changed to dark red. The solvent was removed on a rotary
evaporator. The residue was then chromatographed on alumina oxide with ethyl acetate/
petroleum ether. A red band was eluted with 6:4 ethyl acetate/ petroleum ether mixture and it
was identified as 2 (65%). Single crystals of 2 were obtained by slow diffusion of diethyl ether
into a saturated solution of the complex in ethyl acetate. Mp: 262 °C. Anal. Calcd for
C52H42ClN6OP2RuS2: C, 63.86; H, 4.33; N, 8.59; S, 6.56%. Found: C, 63.92; H, 4.38; N, 8.66; S,
6.26%. IR (KBr discs, cm−1): 3430, 3204 (m, νNH); 1574 + 1482 (s, νC=N + νC−N); 749 (s, νC−S).
1H NMR (400 MHz, DMSO-d6, ppm): 6.55 (t, 2H, J = 8.0 Hz, Ar H), 6.45 (t, 2H, J = 8.0 Hz, Ar
H), 6.62 (t, 1H, J = 7.6 Hz, Ar H), 6.89−6.86 (m, 1H, Ar H), 7.63−7.10 (m, 8H, Ar H), 7.91 (s,
1H, NHterminal), 8.41 (d, 1H, J = 8.1 Hz, −CH=N). 13C NMR (100 MHz, DMSO-d6, ppm): 125.26
(Ar C), 125.55 (Ar C), 127.44 (Ar C), 128.01 (Ar C), 128.78 (Ar C), 128.85 (Ar C), 129.01 (Ar
C), 129.12 (Ar C), 129.87 (Ar C), 132.94 (Ar C), 133.36 (Ar C), 133.56 (Ar C), 135.60 (Ar C),
135.70 (Ar C), 136.05 (Ar C), 136.24 (Ar C), 137.24 (Ar C), 137.43 (Ar C), 138.82 (Ar C),
31
138.91 (Ar C), 140.13 (−CH=N), 170.12 (C−S). P NMR (162 MHz, DMSO-d6, ppm): δ 28.78
(s, PPh2). ESI-MS: m/z = 978.57 [M]+.
2.6 Synthesis of [RuCl(CO)(AsPh3)(PNO-THy)] (3)
A suspension of [RuHCl(CO)(AsPh3)3] (0.2 g, 0.184 mmol) in ethanol (30 mL)
was treated with 2-(2-(diphenylphosphino)benzylidene)-2-thiophene carboxylic acid hydrazone
(0.072 g, 0.184 mmol) and the mixture was gently refluxed for 8h. During this time the color

changed to orange. The solvent was reduced to half of the volume on a rotary evaporator, and the
suspension was filtered, washed thoroughly with cold ethanol (10 mL) and diethyl ether (2 х 20
mL). The product was finally dried under vacuo. Crystals suitable for X-ray diffraction were
obtained by slow evaporation of a concentrated solution of 3 in CH2Cl2/C2H5OH. Yield 81%
(0.163 g), Mp: 120−122 °C. Anal. Calcd for C43H33AsClN2O2PRuS: C, 58.41; H, 3.76; N, 3.17;
S, 3.63. Found: C, 58.62; H, 3.82; N, 3.31 S, 3.69. IR (KBr disks, cm−1): 3323 (m, νNH); 1946 (s,
1
νC≡≡O); 1592 + 1480 (s, νC=N + νC−N); 1274 (s, νC-O); 1432, 1091, 695 (s, for AsPh3). H NMR
(400 MHz, DMSO-d6, ppm): 6.37 (td, 1H, J = 7.2, 1.2 Hz, Ar H), 7.10−7.52 (m, 29H, Ar H),
7.67 (dd, 1H, J = 3.6, 1.2 Hz, Ar H), 8.12 (d, IH, J = 3.6 Hz, −CH=N), 8.93 (s, 1H, Ar H).
13NMR (100 MHz, DMSO-d6, ppm): 124.10 (Ar C), 128.50 (Ar C), 128.67 (Ar C), 129.92 (Ar
C), 130.5 (Ar C), 133.80 (Ar C), 133.20 (Ar C), 133.41 (Ar C), 133.560 (Ar C), 133.92 (Ar C),
31
143.40 (CH=N), 149.23 (C−O), 200.12 (C≡O). P NMR (162 MHz, DMSO-d6, ppm): 32.19 (s,
PPh2). ESI-MS: m/z = 848.57 [M–Cl]+.
2.7 Typical procedure for N-alkylation of (hetero)aromatic amines with alcohols
In a 25 mL round bottomed flask were placed 0.5 mol % of ruthenium(II) catalyst, 2
mmol of alcohol, 2 mmol of amine, 50 mol % of KOH and 2 mL of toluene. The reaction flask
was heated at 100 °C for 12 h in an oil bath. Upon completion (as monitored by TLC), the
reaction mixture was cooled at ambient temperature, H2O (3 mL) was added and the organic
layer was extracted with CH2Cl2 (3 х 10 mL). The combined organic layers were dried with
magnesium sulfate and concentrated. The crude product was purified by column chromatography
(ethyl acetate/n-hexane). Reported isolated yields are an average of two runs.
3. Results and discussion
The ligand precursors (PNO-Thy and PNS-Ph) were synthesized by condensation of 2-
diphenylphosphinebenzaldehyde with 2-thiophenecarboxylic acid hydrazide and 4-phenyl-3-
thiosemicarbazide respectively, following the published procedure (Scheme 1) [47]. The
reactions of the isolated ligands with equimolar amounts of cis-[RuCl2(dmso)4] and
[RuHCl(CO)(AsPh3)] yielded the substituted products 1-3 respectively (Scheme 2). These Ru
complexes are air stable, were obtained in good yield (64–85%), and were characterized by
analytical, spectroscopic methods (IR, 1H, 13C, 31P-NMR and ESI-MS) and X-ray

crystallography for 2 and 3 as described further below. The analytical data of the complexes
agreed well with the proposed molecular formulae. Positive ion ESI-MS analysis of the isolated
products showed an intense peak for [M]+ (m/z 927.81(1), m/z 978.57 (2)) or [M−Cl]+ (m/z
848.57 (3), which confirming the proposed nature of these complexes.
H
H
S
N
N
H
H2N
N
P
O
H2N
S
P
O
N
S
P
N
C2H5OH, CH3COOH
reflux 3h
C2H5OH, CH3COOH
reflux 3h
HN
HN
NH
O
S
PNO-THy
PNS-Ph
Scheme 1 Synthesis of phosphino hydrazone and thiosemicarbazone ligands.
N
R
N
[RuHCl(CO)(AsPh3)3]
Cl
X
cis-[RuCl2(dmso)4]
P
P
Ph
Ph
Ph
P
N
N
Ru
N
Ph
Ethanol, Reflux, 8h
R
P
X
Ethanol, Reflux, 6h
N
Ru
S
HN
O
Ph3As
R
N
O
X
(3)
1; X=O, R=
2; X=S, R=NHC6H5
PNO-THy; X=O, R=
PNS-Ph; X=S, R=NHC6H5
S
S
Scheme 2 Synthesis of ruthenium(II) complexes.
3.1 Crystal structure of the complexes
The crystal structure of the complexes 2 and 3 along with their numbering scheme are
given in figures 1 and 2. Crystallographic data and bond parameters are given in table 1. Single
crystals of 2 were obtained by slow diffusion of diethylether into a saturated solution of the
complex in ethyl acetate. A dark red crystal of approximate dimensions 0.23 х 0.04 x 0.03 mm
was isolated and the single crystal X-ray diffraction experiments were carried out at 295 K. From
the unit cell dimensions, it is clear that the crystal is monoclinic belonging to the I12/a1 space
group. The two PNS-Ph ligands around the metal centre in 2 are arranged in a mer–mer

configuration with the two nitrogen atoms trans to one another and the two phosphorus and two
sulfur atoms in a cis configuration. The average Ru–P, Ru–N and Ru–S bond lengths in 2 are
2.30, 2.06 and 2.37 Å respectively, which compare well to those observed in related RuII
complexes [43a] The average cis angles are S(1)−Ru(1)−S(1) = 87.24(8)°, P(1)−Ru(1)−S(1) =
88.66(5)°, P(1)−Ru(1)−P(1), 98.12(5)°, N(1)−Ru(1)−S(1) = 91.35(8)° and N(1)−Ru(1)−P(1) =
93.10(8)° respectively. The trans angles P(1)−Ru(1)−S(1) = 173.21(3)° and N(1)−Ru(1)−N(1) =
169.95(16)° deviate from linearity. The variations in bond lengths and angles lead to a
significant distortion from an ideal octahedral geometry for the complex.
The complex 3 was crystallized in monoclinic crystal system with the space group P2(1).
The phosphino hydrazone ligand is coordinated to ruthenium by utilizing its phosphorous,
azomethine nitrogen and hydrazone oxygen atom. The O(2)-Ru(1)-P(1) [170.73(7)°], N(1)-
Ru(1)-As(1) [164.12(8)°] and C(1)-Ru(1)-Cl(1) [174.11(11)] trans angles deviate significantly
from linearity and N,O chelation (five member ring) leads to N(1)-Ru(1)-O(2) bite angle,
77.68(10)°. This has resulted in significant distortion in RuCONOPAs core from the ideal
octahedral geometry. All the Ru-ligand distances, namely Ru(1)-C(1) 1.936(4) Å, Ru(1)-N(1)
2.061 (3) Å, Ru(1)-P(1) 2.2969(9) Å, Ru(1)-O(2) 2.099 (2) Å, Ru(1)-As(1) 2.4777 (6) Å and
Ru(I)-Cl(1) 2.4061(10) Å are comparable with those found in complexes reported earlier. The
large deviation of the [P(1)−Ru(1)−P(2)] angle [99.78(3)] from 90 may be ascribed to the steric
repulsion between the two adjacent bulky phosphine and arsine molecules.
3.2 Spectral studies
The IR spectra of the ligands and the corresponding complexes provided significant
information’s about the metal ligand bonding. A strong vibration observed at 1594−1583 cm-1 in
the ligands corresponding to νC=N was shifted to 1592−1572 cm-1 in all the complexes indicating
the participation of azomethine nitrogen in bonding [43c]. A sharp band observed at 1685 cm-1
and 744 cm-1 ascribed to νC=O/ C=S
in the ligands, has completely disappeared in the spectra of the
ν
new Ru complexes and the appearance of a new band at 1276-1274 cm-1 and 749 cm-1 due to
νC−O/νC−S indicate the coordination of the oxygen/sulfur atom after enolisation followed by
deprotonation [48]. The complex 3 displayed a medium to strong band in the region 1946 cm-1,
which is attributed to the terminally coordinated carbonyl group and is observed at a slightly
higher frequency than in the precursor complexes. The IR spectra of all the complexes therefore

confirms the coordination mode of the phosphino-hydrazone/thiosemicarbazone ligand to the
ruthenium(II) ion via the azomethine nitrogen, the imidolate oxygen/thiolate sulfur and the
phosphorous, along with the presence of triphenylarsine group.
1
The H NMR spectra of the ligands and their complexes (1−3) show the signals in the
expected regions. The singlet’s that appeared for the N–NH–C=X (X=O or S) proton of the free
ligands at 11.98−11.94 ppm are absent in the complexes, supporting the enolization and
coordination of the imidolate oxygen or thiolate sulphur to the Ru(II) ion. The doublet due to
azomethine proton (8.46−8.12 ppm) in the complexes are slightly downfield compared to the
13
free ligands (8.85−8.79 ppm), suggesting deshielding upon coordination to Ru(II) ion. The C
NMR spectra show the expected signals in the appropriate regions. For the uncoordinated
ligands, the C=N and C=O/C=S signals appear in the regions around 149.52−141.07 ppm and
158.12/175.81 ppm. Upon coordination and formation of the new Ru complexes, a downfield
shift is observed for the signals of the C=N (143.40-138.91ppm), while the C-O/C-S carbon atom
signals are appeared in the region between 161.80−149.23 and 170.12 ppm. This is consistent
with the PNO/PNS coordination and enolization of the C=O/C=S of hydrazone and
thiosemicarbazone moieties. The C≡O carbon resonating at 200.12 ppm is comparable with
earlier observations (for complex 3) [43b]. The presence of a residual phosphine coordinated to
Ru(II) ion is confirmed by 31P NMR. The singlet observed at 32.19−28.78 ppm in complexes 1–
3, suggested the presence of phosphine heads in the hydrazone and thiosemicarbazone chains.
These signals are very significantly shifted downfield compared with the corresponding free
ligands (~40 ppm), being indicative of coordination through to the phosphorus atom [7].
3.3 Catalytic N-alkylation of amines
Initial studies were performed using 2-aminobenzothiazole and benzyl alcohol as
building blocks and toluene as the solvent, under various reaction conditions and the results are
depicted in Table 3. To ensure its catalytic role, a control experiment was performed in the
absence of base or ruthenium catalyst and, as expected, there was no reaction even after a
prolonged reaction time of 12 h (entries 1 and 9). Using K2CO3, Na2CO3, NaOH and KOtBu as
alternative base for the reaction, decreases in the yield were observed (entries 2–4 and 8).
Furthermore, considering the results when 0.5 mol% of catalyst was used, it is clear that
ruthenium complexes containing phosphino hydrazone ligand (Entry 11) lead to higher yields

than the other two ruthenium catalysts (Entries 6 and 10). This behavior indicates that the steric
effects or the lack of a vacant coordination site due to bischelation of ligands around the metal
centre may play an important role in terms of catalyst efficiency or in terms of generation of the
catalytically active species.
On the basis of the results obtained complex 3 shows relatively better catalytic activity
among the three complexes. Hence, complex 3 was selected as the model catalyst for the
regioselective N-alkylation of various heterocyclic amines, diamines with alcohols to afford the
corresponding secondary amines; the results are summarized in Table 4. When an equimolar
solution of 2-aminobenzothiazoles and 4-methylbenzyl alcohol with 0.5 mol % of 3 in toluene
was used, the reaction went smoothly to afford the expected N-(4-methylbenzyl)benzo[d]thiazol-
2-amine in excellent isolated yield (86%). 2-aminobenzothiazoles efficient alkylated with
benzylalcohol containing electron-donating substituents. The reaction of 2- aminobenzothiazoles
with 4-methoxybenzyl alcohol gave N-(methoxybenzo[d] thiazol-2-amine in 81% isolated yield.
Similarly, the N-alkylation of 2- aminobenzothiazoles and 4-chlorobenzyl alcohol yielded N-(4-
chlorobenzyl)benzo[d]thiazol-2-amine (98%). The N-alkylation with 2-bromo benzyl alcohol
proceeded to give the corresponding product with excellent yield as well (72%). The reaction
was also applied to 2-pyridylmethanol, affording the desired product with 96% yield. The
compatibility of the catalytic system with heterocyclic diamine was demonstrated, and very good
result was obtained for the N,N’-dialkylation of 2,6-diaminopyridine (Entry 4) with
benzylalcohol using the catalyst 3. Reaction of o-phenylenediamine with benzyl alcohol afforded
the desired 2-substituted benzimidazole in 76% (Entry 5) isolated yield.
A possible catalytic cycle is proposed in Scheme 3 on the basis of the results obtained
and available literature on similar ruthenium-catalyzed transformations [40]. This catalysis is
considered to proceed via the (benzyloxy)ruthenium intermediate I, which undergoes β-hydrogen
elimination to give the ruthenium hydride II and R1CHO. Dehydrative condensation of R1CHO
with amine forms R1CH=NR2. Insertion of R1CH=NR2 into the Ru−H bond of II, followed by
alcoholysis of the resulting (amido)ruthenium species III, affords R1CH2NHR2 as the N-
alkylation product and reproduces the (benzyloxy)ruthenium intermediate I and completes the
catalytic cycle.

4. Conclusions
Three new ruthenium(II) phosphino-hydrazone/thiosemicarbazone complexes have been
designed and synthesized by the reactions of cis-[RuCl2(dmso)4] or [RuHCl(CO)(AsPh3)3] with
deprotonated PNO-THy/PNS-Ph. The structure of the complexes (2 and 3) were established by
X-ray crystallography and spectroscopic methods. Single crystal XRD upshots of complexes
revealed
a
distorted octahedral geometry around the ruthenium ion with
hydrazone/thiosemicarbazone acts as a monoanionic tridentate PNS donor fashion. The catalytic
study of complexes 1-3 towards regioselective N-alkylation reactions amines was completed,
showing that all catalysts are active toward catalytic transformations. Notably, complex 3 was
found to be very efficient catalysts toward N-alkylation of a wide range of heterocyclic amines
with alcohols. This catalysis provides a clean, convenient and practical route for the direct N-
alkyl amine synthesis in view of the following advantages: (1) The reaction proceeds smoothly
and effectively under mild conditions. (2) The catalyst is readily available, cheap and stable that
offers easy handling and ready work-up. (3) The present method is applicable in the synthesis of
various N-alkyl amines, including useful aromatic and heteroaromatic amines, in high yields.
Acknowledgment
The authors are grateful to Punjab University, Chandigarh, for providing instrumental facilities.
Appendix A. Supplementary data
Experimental procedure and spectral data for N-alkylated products. CCDC reference number
1588881 and 1588827 for complexes 2 and 3. This data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Supplementary data associated with this article can be found, in the online version, at http://

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H
H
S
N
N
H
H2N
N
P
O
H2N
S
P
O
N
S
P
N
C2H5OH, CH3COOH
reflux 3h
C2H5OH, CH3COOH
reflux 3h
HN
HN
NH
O
S
PNO-THy
PNS-Ph
Scheme 1. Synthesis of phosphino-hydrazone and thiosemicarbazone ligands.
N
R
N
[RuHCl(CO)(AsPh3)3]
Cl
X
cis-[RuCl2(dmso)4]
P
P
Ph
Ph
Ph
P
N
N
Ru
N
Ph
Ethanol, Reflux, 8h
R
P
X
Ethanol, Reflux, 6h
N
Ru
S
HN
O
Ph3As
R
N
O
X
3
1; X=O, R=
2; X=S, R=NHC6H5
PNO-THy; X=O, R=
PNS-Ph; X=S, R=NHC6H5
S
S
Scheme 2. Synthesis of ruthenium(II) complexes.

Fig. 1. Molecular structure of [Ru(PNS-Ph)2] (2) with thermal ellipsoids at the 50 % probability
level.

Fig. 2. Molecular structure of [RuCl(CO)(AsPh3)(PNO-THy)] (3) with thermal ellipsoids at the
50 % probability level. The disordered chloride, carbonyl and thiophene group of the structure
have been omitted for clarity.

CO
X
N
P
Ru
Ph3As
Cl
KOH
-H2O
-KCl
R1
OK
R1
OH
Ph
Ph
P
R2
CO
X
N
R2
N
N
N
H
P
Ru
HN
R
P
S
Ph3As
O
X
I
R1
OH
R
R1
O
Ph3As
R1
N
CO
P
N
Ru
R2
R2NH2
H2O
P
X
Ru
X
OC
N
Ph3As
H
II
III
R2
N
R2
H
Scheme 3. Plausible mechanism for N-alkylation of amines.

Highlights
 Ru(II) complexes with PNO/PNS donor ligands were designed and synthesized.
 The complexes efficiently catalyzed the N-alkylation of amines with alcohols.
 Water as a sole by product in this novel catalytic reactions.

Graphical Abstract Pictogram
Ru Catalyzed N-Alkylation of Amines
NH2
NH2
S
NH2
N
Cl
Ru
Toluene,
KOH, 12h
-H2O
Toluene,
KOH,12h
Ru
P
N
N
R
OH
R
R
OH
-H2O
Ru
S
As
Ph3
O
H
R
S
N
C
NH
O
N
N
0.5 mol %

Graphical Abstract Synopsis
Ruthenium(II) complex bearing PNO ligand efficiently catalyses the N-alkylation of amines with
alcohols. The reaction works under mild condition with 0.5 mol % of catalyst and could be
performed on a small scale, providing an alternative to conventional alkylation reaction.

Highlights
 Ru(II) complexes with PNO/PNS donor ligands were designed and synthesized.
 The complexes efficiently catalyzed the N-alkylation of amines with alcohols.
 Water as a sole by product in this novel catalytic reactions.

Table1 Crystal, measurement and refinement data for complexes 2 and 3
2
C52H42N6P2RuS2
978.04
3
C43H33AsClN2O2PRuS
884.18
Formula
Fw
monoclinic
I 1 2/a 1
18.1577(4)
11.2930(3)
22.6297(5)
90
101.712()
90
4543.7(2)
4
Cryst syst
Space group
a, Å
b, Å
c, Å
Triclinic
PĪ
11.1690(3)
18.3688(8)
20.2066(6)
68.206(3)
87.070(2)
77.349(3)
3753.8(2)
4
α, deg
β, deg
γ, deg
Vol, Å3
Z
F(000)
2008
1.430
4.661
1784
1.565
1.565
Dcalcd, g cm-3
Absorption coefficient
mm-1
4.3850 < 2θ >
67.4040
-21< = h< = 17
-13< = k< = 13
-17< = l< = 26
Scan range for data
collection (deg)
Index ranges
3.58 to 29.14
-11< = h< = 13
-16< = k< = 21
-24< = l< = 23
24015, 12983, 0.0548
Reflections
29559/13249,0.0361
collected/unique, Rint
Completeness to thetamax
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I >2σ(I)]a
0.978
3654/0/273
1.081
0.997
13249/0/990
1.033
R1 =0.0384,
wR2 = 0.0828
R1 = 0.0584,
wR2 = 0.0828
0.0430, 0.1261
R indices (all data)
0.0504, 0.1261

Table 2 Selected bond lengths and bond angles for the complexes 2 and 3
2
3
Interatomic distances (Å)
Ru(1)−C(1)
Ru(1)−N(1)
1.936(4)
2.061(3)
Ru(1)-S(1)
Ru(1)-S(1)
2.372(8)
2.3871(8)

Ru(1)−P(1)
2.2969(9)
2.099(2)
2.4777(4)
2.4061(10)
Ru(1)-P(1)
Ru(1)-P(1)
Ru(1)-N(1)
Ru(1)-N(1)
2.3080(8)
2.3080(8)
2.065(3)
2.065(3)
Ru(1)−O(2)
Ru(1)−As(1)
Ru(1)−Cl(1)
Bond angles(ᵒ)
Cl(1)−Ru(1)−As(1) 86.26(3)
S(1)-Ru(1)-S(1) 87.24(5)
P(1)-Ru(1)-S(1) 87.46(3)
P(1)-Ru(1)-S(1) 173.21(3)
P(1)-Ru(1)-S(1) 173.21(3)
P(1)-Ru(1)-S(1) 172.06(5)
P(1)-Ru(1)-P(1) 98.12(4)
N(1)-Ru(1)-S(1) 90.40(8)
N(1)-Ru(1)-S(1) 92.32(8)
N(1)-Ru(1)-S(1) 82.32(8)
N(1)-Ru(1)-P(1) 93.10(8)
N(1)-Ru(1)-P(1) 93.10(8)
N(1)-Ru(1)-N(1) 169.95(16)
P(1)−Ru(1)−As(1)
P(1)−Ru(1)−Cl(1)
O(2)−Ru(1)−As(1)
O(2)−Ru(1)−P(1)
N(1)−Ru(1)−As(1)
N(1)−Ru(1)−P(1)
N(1)−Ru(1)−O(2)
C(1)−Ru(1)−As(1)
C(1)−Ru(1)−Cl(1)
C(1)−Ru(1)−P(1)
C(1)−Ru(1)−N(1)
101.14(3)
94.51(3)
88.08(6)
170.73(7)
164.12(8)
93.26(8)
77.68(10)
96.16(10)
174.11(11)
90.30(11)
90.35(13 )
Table 3 N-alkylation of 2-aminobenzothiazole with benzyl alcohol under various
conditionsa
Catalyst
(mol%)
1.00
1.00
1.00
Yield
(%)b
0
35
43
Entry Catalyst
Base
1
2
3
4
5
-
1
1
1
1
1
K2CO3
Cs2CO3
NaOH
KOH
1.00
1.00
55
62