Ruthenium(II) carbonyl complexes bearing quinoline-based NNO tridentate ligands as catalyst for one-pot conversion of aldehydes to amides and o-allylation of phenols

Article abstract of DOI:10.1016/j.saa.2013.07.114

(Chemical Equation Presented) Six new octahedral ruthenium(II) carbonyl complexes having the general molecular formula [RuCl(-CO)(B)L^1-2] (B = PPh₃, AsPh₃ or py; L^1-2 = quinoline based NNO ligand) were synthesized. The quinoline based ligands behave as monoanionic tridentate donor and coordinated to ruthenium via ketoenolate oxygen, azomethine nitrogen and quinoline nitrogen. The composition of the complexes has been established by elemental analysis and spectral methods (FT-IR, electronic, ¹H NMR, ¹³C NMR, ³¹P NMR and ESI-Mass). The complexes were used as efficient catalysts for one-pot conversion of various aldehydes to their corresponding primary amides in presence of NH ₂OH·HCl and NaHCO₃. The effect of catalyst loading and reaction temperature on catalytic activity of the ruthenium(II) carbonyl complexes were also investigated. The synthesized complexes also possess good catalytic activity for the o-allylation of phenols in the presence of K ₂CO₃ under mild conditions. The complexes afforded branched allyl aryl ethers according to a regioselective reaction.

Full text of DOI:10.1016/j.saa.2013.07.114

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 501–508
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Ruthenium(II) carbonyl complexes bearing quinoline-based NNO
tridentate ligands as catalyst for one-pot conversion of aldehydes
to amides and o-allylation of phenols
⇑
R. Manikandan, G. Prakash, R. Kathirvel, P. Viswanathamurthi
Department of Chemistry, Periyar University, Salem 636 011, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Ruthenium(II) carbonyl complexes containing quinoline based NNO tridentate ligands were synthesized
and characterized. They have been assigned an octahedral structure. The new complexes were found to
be efficient catalyst for aldehydes to amides and o-allylation of phenols.
ꢀ
ꢀ
ꢀ
ꢀ
Six new Ru(II) carbonyl complexes
with quinoline based ligands were
synthesized.
Spectral and elemental data have
used to prove the binding modes in
complexes.
Catalytic efficiency of the complexes
in aldehyde to amide reaction was
evaluated.
The complexes have used as catalyst
for the synthesis of allyl aryl ethers.
O
OAr
H
Ph
(Branched)
+
R
NH2OH.HCl
+
Ph
OAr
H3
C
CO
Ru
(Linear)
N
O
N
NaHCO3; MeCN
K
2CO3; MeCN
Cl
O
R
B
ArOH
NH2
+
Ph
Cl
R
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 11 July 2013
Received in revised form 24 July 2013
Accepted 31 July 2013
Available online 9 August 2013
Six new octahedral ruthenium(II) carbonyl complexes having the general molecular formula [RuCl(-
CO)(B)L1–2] (B = PPh3, AsPh3 or py; L1–2 = quinoline based NNO ligand) were synthesized. The quinoline
based ligands behave as monoanionic tridentate donor and coordinated to ruthenium via ketoenolate
oxygen, azomethine nitrogen and quinoline nitrogen. The composition of the complexes has been estab-
lished by elemental analysis and spectral methods (FT-IR, electronic, 1H NMR, 13C NMR, 31P NMR and ESI-
Mass). The complexes were used as efficient catalysts for one-pot conversion of various aldehydes to their
corresponding primary amides in presence of NH2OHÁHCl and NaHCO3. The effect of catalyst loading and
reaction temperature on catalytic activity of the ruthenium(II) carbonyl complexes were also investi-
gated. The synthesized complexes also possess good catalytic activity for the o-allylation of phenols in
the presence of K2CO3 under mild conditions. The complexes afforded branched allyl aryl ethers accord-
ing to a regioselective reaction.
Keywords:
Quinoline based ligand
Ruthenium(II) carbonyl complexes
Aldehydes to amides conversion
o-Allylation of phenols
Ó 2013 Elsevier B.V. All rights reserved.
Introduction
prepared and studied extensively. The central metal in these
complexes act as active sites and thereby successfully catalyze
A large number of transition metal complexes with a variety of
acyclic [1–3] and macrocyclic [4–6] Schiff bases have been
chemical reactions [7,8]. The Schiff base transition metal
complexes are a family of attractive oxidation catalysts for a vari-
ety of organic substrates because of their cost effective synthesis,
chemical and thermal stability. They are also used to catalyze
transformation of simple organic substrates to functionalised
⇑
Corresponding author. Tel.: +91 944 3775719; fax: +91 427 2345124.
E-mail address: viswanathamurthi72@gmail.com (P. Viswanathamurthi).
1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2013.07.114

502
R. Manikandan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 501–508
derivatives of commercial and synthetic interest [9–12]. Among
the transition metal complexes, the synthesis of ruthenium(II)
complexes containing oxygen and nitrogen donor Schiff base is of
significant importance due to their multi-electron transfer proper-
ties, ability to have a wide range of oxidation states and potential
catalytic activity [13–15]. In particular, triphenylphosphine and
triphenylarsine ligands are known to stabilize the lower oxidation
states of ruthenium in their carbonyl complexes [16].
Amides are one of the most important and prolific functional
groups, with a great importance in both research and industrial
chemistry due to their prevalence in detergents, lubricants, biolog-
ically active compounds and pharmaceuticals [17]. Although, there
are many strategies to prepare them, enormous amount of wastes
generated by the standard protocols forces the industry to look for-
ward for better strategies [18]. The Beckmann type rearrangement
[19] is a very efficient approach for the preparation of amides. In
Experimental
Materials and methods
All the reagents used were chemically pure and AR grade. The
solvents were purified and dried according to standard proce-
dures [47]. RuCl3Á3H2O was purchased from Loba Chemie Pvt
Ltd., India. The starting complexes [RuHCl(CO)(PPh3)3],
[RuHCl(CO)(PPh3)2(Py)] and [RuHCl(CO)(AsPh3)3] were prepared
according to the literature methods [48–50]. Microanalyses of
carbon, hydrogen and nitrogen were carried out using Vario EL
III Elemental analyzer at SAIF – Cochin India. The IR spectra of
the ligands and their complexes were recorded as KBr pellets
on a Nicolet Avatar model spectrophotometer in 4000–400 cmÀ1
range. Electronic spectra of the ligands and their complexes have
been recorded in dichloromethane using a Shimadzu UV-1650 PC
spectrophotometer in 800–200 nm range. 1H, 13C and 31P NMR
spectra were recorded in Jeol GSX-400 instrument using DMSO-
d6 as the solvent. 1H NMR and 13C NMR spectra were obtained
at room temperature using TMS as the internal standard. 31P
NMR spectra of the complexes were obtained at room tempera-
ture using o-phosphoric acid as a reference. The ESI-MS spectra
were recorded by LC-MS Q-ToF Micro Analyzer (Shimadzu) in
the SAIF, Panjab University, Chandigarh. Melting points were re-
corded on a Technico micro-heating table and are uncorrected.
The catalytic yields were determined using ACME 6000 series
GC-FID with DP-5 column of 30 m length, 0.53 mm diameter
fact, about 3.8 million tons per year of e-caprolactam is produced
through this process, starting from the corresponding ketoximine
[20]. The similar reaction with aldoximes is, however, more chal-
lenging [21], with the dehydration reaction to give nitriles being
the main process.
Besides all aforementioned drawbacks, Raney’s nickel transfor-
mation of aldoximes to amides was introduced as early as 1937
[22]. The other organometallics being recently tested in a similar
protocol, including those derived from boron [23], nickel [24], cop-
per [24,25], ruthenium [26], rhodium [27], palladium [28] and
bimetallic species containing cobalt–zinc [29] and silver–gold
[30] combinations. However, the preparation of starting aldoxime
usually needed stoichiometric amounts of acids, as catalyst, and
use of hydroxylamine reagent in large excess, therefore, this ap-
proach had still possibilities to be improved [31]. In fact, the direct
one-pot protocol, starting from nearly equimolecular amounts of
aldehydes and hydroxylammonium derivatives, has been recently
introduced, using catalysts derived from copper [32], zinc, indium
[33], ruthenium [34], rhodium [35] and palladium [36].
Aryl ethers are common subunits of biologically active mole-
cules. A part from their use as precursors for the Claisen rearrange-
ment [37,38], aryl allyl ethers have not been used extensively as
building blocks for natural product synthesis because methods
for their enantioselective construction are limited. Two reports of
stereospecific allylic etherification of branched carbonates cata-
lyzed by Ru [39] and Rh [40,41] were reported, and a few enantio-
selective palladium-catalyzed examples have also been reported
[42,43]. Elegant applications of the palladium-catalyzed chemistry
for the synthesis of natural products demonstrate the potential of
asymmetric allylic etherification in organic synthesis [44]. Thus,
new, more general, regioselective methods for the construction
of allylic ethers would be synthetically valuable.
and 5.00 lm film thickness.
General procedure for the preparation of quinoline based ligands
(HL1–2
)
8-Aminoquinoline (0.4 g, 2.8 mmol), pentane-2, 4-dione (0.56 mL,
5.6 mmol) or 1-phenyl-1, 3-butanedione (0.45 g, 2.8 mmol),
activated molecular sieves (0.5 g), toluene (20 mL) and 7 drops of
formic acid were added to a flask equipped with magnetic stirring
bar. The mixture was refluxed under stirring for 40 h and then
cooled to room temperature. The molecular sieves were filtered
off and washed with toluene (3 Â 10 mL). The combined organic
solution was washed with saturated brine and water successively
and then dried over NaSO4. The NaSO4 was removed by filtration
and volatiles were removed from the filtrate by rotary evapora-
tion to give yellow powder. Recrystallisation of the solid from
mixture of dichloromethane and n-hexane generated pale yellow
crystals [51].
Compound HL1
In contrast to the considerable growth of literature on the
chemistry of quinoline based Schiff base complexes, to the best
of our knowledge there are no reports available for catalytic trans-
formation of aldehydes to amides and o-allylation of phenols by
ruthenium(II) carbonyl complex containing quinoline based Schiff
base ligand. Hence in continuation of our research on the synthesis
and catalytic applications of ruthenium(II) and ruthenium(III)
complexes [45,46] and in view of interesting coordination modes
of quinoline-based NNO ligands with ruthenium metal complexes,
we herein describe new ruthenium(II) carbonyl complexes with
substituted 8-aminoquinoline diketone ligands incorporated with
chloride and PPh3/AsPh3/pyridine as ancillary ligands. All the com-
plexes have been characterized by analytical and spectral methods.
The applications of these complexes as homogeneous catalyst for
the one pot conversion of aldehydes to corresponding primary
amides using NH2OHÁHCl and o-allylation of phenols were also
investigated.
Yield: 0.50 g (79%), yellow, m.p. 80 °C. Anal. Calcd for C14H14N2-
O:C 74.31; H 6.23; N 12.38%. Found:C 74.82; H 6.26; N 12.90%. IR
(KBr, cmÀ1):1692 (C@O), 1662 (C@N), 1596 (ring C@N). UV (kmax,
CH2Cl2):390, 310, 250. 1H NMR (400 MHz, DMSO-d6, d, ppm):13.24
(s, 1H, OH), 8.94–8.93 (d, J = 4.8 Hz, 1H, Ar), 8.41–8.38 (d, J = 8.4 Hz,
1H, Ar), 7.71–7.54 (m, 4H, Ar), 5.37 (s, 1H, CH), 2.27 (s, 3H, CH3),
2.05 (s, 3H, CH3).
Compound HL2
Yield: 0.61 g (76%), yellow, m.p. 120 °C. Anal. Calcd for C19H16-
N2O:C 79.14; H 5.59; N 9.71%. Found:C 78.78; H 5.62; N 9.73%. IR
(KBr, cmÀ1): 1694 (C@O), 1663 (C@N), 1595 (ring C@N) UV
(kmax, CH2Cl2):384, 305, 253. 1H NMR (400 MHz, DMSO-d6, d,
ppm):10.78 (s, 1H, OH), 8.94–8.92 (d, J = 9.2 Hz, 1H, Ar), 8.67–
8.65 (d, J = 7.2 Hz, 1H, Ar), 8.59–7.52 (m, 9H, Ar), 6.57 (s, 1H,
CH), 2.19 (s, 3H, CH3).

R. Manikandan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 501–508
503
General procedure for synthesis of new ruthenium(II) carbonyl
complexes
(400 MHz, DMSO-d6, d, ppm): 8.94–8.93 (d, J = 4.2 Hz, 1H, Ar),
8.68–8.65 (d, J = 8.8 Hz, 1H, Ar), 8.59–6.98 (m, 19H, Ar), 5.75 (s,
1H, CH), 2.01 (s, 3H, CH3), 1.38 (s, 3H, CH3). 13C NMR
(400 MHz,DMSO-d6, d, ppm):205.23 (CBO), 193.57 (CAO), 172.24
(C@N), 138.95–128.31 (m, ArC), 101.02 (CH), 30.96 (CH3), 22.07
(CH3). MS (ESI), m/z = 698.1 [M+].
All new metal complexes were synthesized according to follow-
ing general procedure. To a solution of [RuHX(CO)(EPh3)2(B)]
(X = H or Cl; E = P or As; B = PPh3, AsPh3 or Py) (0.0769 g–
0.1084 g; 0.1 mmol) in benzene (20 mL), the appropriate ligand
(0.0226 g–0.0288 g; 0.1 mmol) was added in 1:1 M ratio. The mix-
ture was heated under reflux for 7 h on water bath. Then the
resulting solution was concentrated to 3 mL and the product pre-
cipitated by the addition of small amount of petroleum ether
(60–80 °C). The resulting complexes were recrystallized from CH2-
Cl2/petroleum ether and dried under vacuum.
[RuCl(CO)(AsPh3)(L2)]6
Yield:0.56 g(75%), Green, m.p. 176 °C. Anal. CalcdforC38H30ClN2-
O2AsRu:C 60.20; H 3.99; N 3.70%. Found:C 60.22; H 3.72; N 3.58%. IR
(KBr, cmÀ1):1955 (CBO), 1621 (C@N), 1571 (ring C@N), 1373 (CAO).
UV (kmax, CH2Cl2):465, 390, 254, 231. 1H NMR (400 MHz, DMSO-d6,
d, ppm):8.66–8.65 (d, J = 4.4 Hz, 1H, Ar), 8.16–8.13 (d, J = 8.4 Hz, 1H,
Ar), 8.0–6.96 (m, 24H, Ar), 6.02 (s, 1H, CH), 2.19 (s, 3H, CH3). 13C NMR
(400 MHz, DMSO-d6, d,ppm):204.75 (CBO), 189.75 (CAO), 168.37
(C@N), 138.72–124.33 (m, ArC), 103.50 (CH), 28.56 (CH3). MS (ESI),
m/z = 758.0 [M+].
[RuCl(CO)(PPh3)(L1)] 1
Yield: 0.52 g (79%), Green, m.p. 270 °C. Anal. Calcd for C33H28-
ClN2O2PRu:C 60.78; H 4.33; N 4.30%. Found:C 60.82; H 4.53; N
4.80%. IR (KBr, cmÀ1):1963 (CBO), 1620 (C@N), 1570 (ring C@N),
1373 (CAO). UV (kmax, CH2Cl2):423, 352, 255, 232. 1H NMR
(400 MHz, DMSO-d6, d, ppm):8.92–8.91 (d, J = 4.4 Hz, 1H, Ar),
8.62–8.60 (d, J = 8.0 Hz, 1H, Ar), 8.39–7.16 (m, 19H, Ar), 5.52 (s, 1H,
CH), 1.38 (s, 3H, CH3), 1.23 (s, 3H, CH3). 13C NMR (400 MHz,DMSO-
d6, d, ppm):204.84 (CBO), 198.78 (CAO), 175.75 (C@N), 136.59–
122.21 (m, ArC), 102.87 (CH), 28.54 (CH3), 22.48 (CH3). 31P NMR
(400 MHz, CDCl3, d, ppm):22.35. MS (ESI), m/z = 652.9 [M+].
Catalytic conversion of aldehydes to amides
Catalytic conversion of aldehydes into their corresponding
amides was carried out by ruthenium(II) carbonyl complexes as
catalyst in the following general procedure. The reaction vessel
was charged with aldehyde (2 mmol), NH2OHÁHCl (2 mmol),
NaHCO3 (2 mmol) and ruthenium catalyst (0.01 mmol) and the
mixture was placed under an atmosphere of nitrogen. About
4 mL of dry and degassed toluene was added and the mixture
was stirred for 15 min at room temperature followed by reflux
for 10 h. On completion of the reaction, 2–3 mL methanol was
added to the mixture followed by filtration through Celite to re-
move catalyst and NaHCO3. The filtrate was subjected to GC anal-
ysis and the product was identified and determined with authentic
samples.
[RuCl(CO)(PPh3)(L2)]2
Yield: 0.53 g (75%), Green, m.p. 246 °C. Anal. Calcd for C38H30-
ClN2O2PRu:C 63.91; H 4.23; N 3.93%. Found:C 63.42; H 4.16; N
3.92%. IR (KBr, cmÀ1):1960 (CBO), 1620 (C@N), 1569 (ring C@N),
1373 (CAO). UV (kmax, CH2Cl2):426, 309, 262, 231. 1H NMR
(400 MHz, DMSO-d6, d, ppm):8.62–8.61 (d, J = 4.2 Hz, 1H, Ar),
8.0–7.98 (d, J = 8.0 Hz, 1H, Ar), 7.85–6.82 (m, 24H, Ar), 6.21 (s,
1H, CH), 2.16 (s, 3H, CH3). 13C NMR (400 MHz, DMSO-d6, d,
ppm):208.12 (CBO), 196.36 (CAO), 168.25 (C@N), 138.52–125.62
(m, ArC), 102.22 (CH), 28.34 (CH3). 31P NMR (400 MHz, CDCl3, d,
ppm): 22.73. MS (ESI), m/z = 714.9 [M+].
o-Allylation of phenols
A 0.3 mL (2 mmol) of cinnamyl chloride was added to a mixture
consisting of 0.42 g (3 mmol, 1.5 equivs.) of K2CO3, 0.023–0.038 g
(0.05 mmol) of ruthenium(II) carbonyl complex, and acetonitrile
(12 mL). Then, phenol (3 mmol, 1.5 equivs.) was added and the
mixture was stirred at room temperature for 40 h. The resulting
slurry was evaporated under vacuum and the residue was ex-
tracted with dichloromethane (20 mL). The collected solution
was filtered. Small amount of NaH was added to the filtrate (to trap
residual phenol) until evolution of gas ceased and the solution was
filtered again. The filtrate was evaporated under vacuum to leave
pale brown oil consisting mixture of expected branched 1-phe-
nyl-1-phenoxy-2-propene and linear aryl ethers, as determined
by 1H NMR spectroscopy [52].
[RuCl(CO)(Py)(L1)]3
Yield: 0.32 g (70%), Green, m.p. 166 °C. Anal. Calcd for C20H18-
ClN3O2Ru:C 51.23; H 3.87; N 8.96%. Found:C 51.73; H 3.76; N
8.91%. IR (KBr, cmÀ1):1944 (CBO), 1615 (C@N), 1560 (ring C@N),
1373 (CAO). UV (kmax, CH2Cl2):415, 380, 262, 231. 1H NMR
(400 MHz, DMSO-d6, d, ppm):8.96–8.95 (d, J = 6.8 Hz, 1H, Ar),
8.58–8.57 (d, J = 3.2 Hz, 1H, Ar), 8.23–6.98 (m, 9H, Ar), 5.91 (s,
1H, CH), 1.38 (s, 3H, CH3), 1.28 (s, 3H, CH3). 13C NMR
(400 MHz,DMSO-d6, d, ppm): 206.43 (CBO), 191.87 (CAO),
178.25 (C@N), 137.29–121.82 (m, ArC), 102.78 (CH), 27.92 (CH3),
25.23 (CH3). MS (ESI), m/z = 468.1 [M+].
[RuCl(CO)(Py)(L2)]4
Yield: 0.37 g (71%), Green, m.p. 154 °C. Anal. Calcd for C25H20-
ClN3O2Ru: C 56.55; H 3.80; N 7.91%. Found: C 56.70; H 3.40; N
7.42%. IR (KBr, cmÀ1): 1943 (CBO), 1604 (C@N), 1580 (ring C@N),
1373 (CAO). UV (kmax, CH2Cl2): 400, 316, 257, 229. 1H NMR
(400 MHz, DMSO-d6, d, ppm): 8.56–8.55 (d, J = 6.4 Hz, 1H, Ar),
8.34–8.33 (d, J = 4.8 Hz, 1H, Ar), 8.60–6.83 (m, 24H, Ar), 5.82 (s,
1H, CH), 1.28 (s, 3H, CH3). 13C NMR (400 MHz, DMSO-d6, d,
ppm):206.52 (CBO), 183.65 (CAO), 174.39 (C@N), 133.56–127.69
(m, ArC), 104.23 (CH), 26.67 (CH3). MS (ESI), m/z = 530.1 [M+].
Results and discussion
Diamagnetic, hexa-coordinated low spin ruthenium(II) carbonyl
complexes of general formula [RuCl(CO)(B)(L1–2)] (B = PPh3, AsPh3
or Py; L1–2 = quinoline based NNO ligand) were synthesized in
quantitative yield from the reaction of [RuHCl(CO)(EPh3)2(B)]
(E = P or As; B = PPh3, AsPh3 or Py) with quinoline ligands in dry
benzene in 1:1 M ratio (Fig. 1). In all these reactions, it was ob-
served that the quinoline based NNO ligands behaved as mononeg-
ative tridentate ligands by replacing two molecules of
triphenylphosphine or triphenylarsine and one molecule of hy-
dride from the starting complexes. All the complexes are green in
color, air stable in both solid and liquid states at room temperature
and are nonhygroscopic. The synthesized ruthenium(II) complexes
are highly soluble in commonly used solvents such as benzene,
[RuCl(CO)(AsPh3)(L1)] 5
Yield: 0.50 g (73%), Green, m.p. 280 °C. Anal. Calcd for C33H28-
ClN2O2AsRu:C 56.95; H 4.05; N 4.03%. Found:C 56.56; H 4.23; N
4.52%. IR (KBr, cmÀ1):1963 (CBO), 1618 (C@N), 1571 (ring C@N),
1374 (CAO). UV (kmax, CH2Cl2):436, 348, 256, 231. 1H NMR

504
R. Manikandan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 501–508
H3C
N
CO
N
N
O
H3C
N
R
Benzene
[RuHCl(CO)(EPh3)2(B)]
+
Ru
B
Reflux 7 h
O
Cl
R
R = CH3 (L1) or C6H5 (L2); E = P or As; B = PPh3, AsPh3 or py
Fig. 1. Schematic representation of synthesis of complexes.
Table 1
Effect of catalyst loading in the one-pot conversion of benzaldehyde to benzamide using complex (1).a
O
O
Complex (1)
NH2OH.HCl
NH2
H
NaHCO3; MeCN
Reflux 12 h
Entry
Amount of complex (1) (mmol)
Yield (%)b
1
2
3
4
5
6
Absence of catalyst
2
24
52
89
91
93
0.005
0.0075
0.01
0.02
0.03
a
Reaction conditions: complex (1), benzaldehyde (2 mmol), NH2OH.HCl (2 mmol) and NaHCO3 (2 mmol) in MeCN (4 mL) refluxed for 12 h under an N2 atmosphere.
The conversion is determined by GC.
b
toluene, chloroform, dichloromethane, acetonitrile, dimethyl form-
amide, and dimethyl sulfoxide, producing intense colored
solutions. The analytical data of all the ruthenium(II) carbonyl
complexes are in good agreement with the molecular structure
as proposed.
100
90
80
70
60
50
40
30
20
Infrared spectroscopic analysis
The FT-IR spectra of the ligands, showed no significant peak in
the region of 3100–3250 cmÀ1 corresponds to free -NH2 group of
quinoline indicated that the formation of Schiff base ligands by
the condensation of amine with diketones [53]. The formation of
Schiff base ligands is also be confirmed by the presence of a peak
in the region 1662–1663 cmÀ1 due to azomethine (>C@N) group.
This band has been shifted to lower frequencies (1604–
1621 cmÀ1) in metal complexes showed that the coordination of
the ligand to ruthenium through the azomethine nitrogen atom.
The band due to C@O appeared around 1692–1694 cmÀ1 in the free
ligands have disappeared and new band appeared around 1373–
1374 cmÀ1 (CAO) on complexation. These observation attributed
to ketoenolization of the ACH2AC@O group and subsequent coor-
dination through the deprotonated oxygen. The band appeared
around 1595–1596 cmÀ1 in ligands are assigned to C@N group of
quinoline. This band has been shifted to lower frequencies around
1560–1580 cmÀ1 in metal complexes indicated that the third coor-
dination is through quinoline nitrogen. Hence, from the infrared
spectroscopic data, it was inferred that azomethine, enolic oxygen
and quinoline nitrogen atoms are involved in the coordination of
0
2
4
6
8
10
12
14
16
18
Time (h)
Fig. 2. Effect of reaction time on the yield of benzaldehyde to benzamide. Reaction
conditions: benzaldehyde (2 mmol), NH2OHÁHCl, NaHCO3 (2 mmol), complex 1
(0.01 mmol) and solvent (4 mL) were refluxed under an N2 atmosphere.
the tridentate Schiff bases to ruthenium ion in all the complexes.
Further the strong absorption around the 1943–1963 cmÀ1 has
been assigned to the terminally coordinated carbonyl group in
the new ruthenium complexes [54]. In the case of complexes
containing coordinated heterocyclic nitrogen bases [55], a medium
intensity band was observed in the region 1028–1029 cmÀ1
.

R. Manikandan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 501–508
505
Table 2
One-pot conversion of aldehydes to amides using various ruthenium(II) complexes as catalyst.
O
O
NH2
H
Ru(II) carbonyl complex
+
NH2OH.HCl
NaHCO3; MeCN
Reflux 10 h
R
R
(R = H, CH3, OCH3, NO2 or Cl)
Aldehydes
Benzaldehyde
Complex
1
Amides
Benzamide
4-Methylbenzamide
4-Methoxybenzamide
4-Nitobenzamide
4-Chlorobenzamide
Benzamide
4-Methylbenzamide
4-Methoxybenzamide
4-Nitobenzamide
4-Chlorobenzamide
Benzamide
4-Methylbenzamide
4-Methoxybenzamide
4-Nitobenzamide
4-Chlorobenzamide
Benzamide
4-Methylbenzamide
4-methoxybenzamide
4-Nitobenzamide
4-Chlorobenzamide
Benzamide
4-Methylbenzamide
4-methoxybenzamide
4-Nitobenzamide
4-Chlorobenzamide
Benzamide
Yield (%)a
87
80
78
91
89
84
78
74
90
86
73
69
63
82
77
72
66
60
80
75
81
76
71
88
84
79
73
68
85
80
4-Methylbenzaldehyde
4-Methoxybenzaldehyde
4-Nitrobenzaldehyde
4-Chlorobenzaldehyde
Benzaldehyde
4-Methylbenzaldehyde
4-Methoxybenzaldehyde
4-Nitrobenzaldehyde
4-Chlorobenzaldehyde
Benzaldehyde
4-Methylbenzaldehyde
4-Methoxybenzaldehyde
4-Nitrobenzaldehyde
4-Chlorobenzaldehyde
Benzaldehyde
4-Methylbenzaldehyde
4-methoxybenzaldehyde
4-Nitrobenzaldehyde
4-Chlorobenzaldehyde
Benzaldehyde
4-Methylbenzaldehyde
4-methoxybenzaldehyde
4-Nitrobenzaldehyde
4-Chlorobenzaldehyde
Benzaldehyde
4-methylbenzaldehyde
4-methoxybenzaldehyde
4-Nitrobenzaldehyde
4-Chlorobenzaldehyde
2
3
4
5
6
4-methylbenzamide
4-methoxybenzamide
4-Nitobenzamide
4-Chlorobenzamide
a
GC yield based on the amount of amides.
Electronic spectroscopic analysis
are assigned to aromatic protons. The peak appeared commonly
at d 5.37–6.57 in both the ligands and complexes have been as-
signed to (ACH@CA) group. In addition, methyl protons appeared
in the region d 1.23–2.27. The new complexes did not show any
signals in the upfield region at d À5 to À12, confirmed the removal
of hydride from the starting complexes. The above observations
made it clear that the quinoline based NNO donor Schiff base li-
gands coordinated with ruthenium ion in all the complexes.
The absorption spectra of all the complexes in dichloromethane
at room temperature showed three to four bands in the region
229–465 nm. The high intensity bands in the region 229–390 nm
were assignable to ligand-centred (LC) transitions and have been
designated as
transitions. In all the complexes the lowest energy bands observed
in the region 400–465 nm were attributed to the Ru(d
) ? L(p*
p–
p* (phenyl ring) and n–p* (azomethine (C@N))
p
)
13C NMR spectroscopic analysis
metal to ligand charge transfer (MLCT) transitions [54]. The fact
that there is essentially no variation in the energy of the MLCT
band suggested that the energy gap between the metal-d
p and
The appearance of peak at 204.75–208.12 ppm region is due to
carbonyl carbon (ACBO). The azomethine carbon (ACH@NA) has
shown their signal around 168.25–178.25 ppm region. The peak
at 183.65–198.78 ppm has been assigned to (@CAOA) carbon.
The multiplets at 121.82–138.95 ppm region were assigned to aro-
matic carbons. The singlet around 101.02–104.23 ppm region
which can be assigned to (ACH@C) carbon. The methyl carbon ap-
peared in the region 22.07–30.96 ppm.
the ligand-p* levels remains constant despite the variation of the
substituent in the complexes. The pattern of the electronic spectra
of all the complexes indicated the presence of an octahedral envi-
ronment around the ruthenium(II) ion, similar to that of other
octahedral ruthenium(II) complexes [56].
1H NMR spectroscopic analysis
1H NMR spectra of the ligands and their complexes were re-
corded to confirm the coordinating modes of the ligands. The spec-
tra of free ligands have shown signal at d 10.28–13.24 which is
characteristic signal of AOH proton, which is absent in the com-
plexes suggesting the coordination through deprotonated oxygen.
The multiplets at d 6.02–8.94 for all the complexes and ligands
31P NMR spectroscopic analysis
31P NMR spectra of some of the complexes were recorded to
confirm the presence of triphenylphosphine group in the com-
plexes. A sharp singlet was observed around 22.35–22.73 ppm
due to presence of triphenylphosphine ligand in the complexes.

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R. Manikandan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 501–508
Table 3
o-Allylation of phenols from cinnamyl chloride using various ruhenium(II) carbonyl complexes as catalyst.
OAr
Ph
1a - b (Branched)
+
Ru(II) complexes
K2CO3; MeCN
ArOH
+
Ph
Cl
Ar
a: phenyl
Ph
OAr
b: p-tolyl
2a - b (Linear)
Complex
1
Allylic chloride
ArOH
Products
Yield (%)a,b
B/Lb
Cinnamyl chloride
Cinnamyl chloride
Cinnamyl chloride
Cinnamyl chloride
Cinnamyl chloride
Cinnamyl chloride
Cinnamyl chloride
Cinnamyl chloride
Cinnamyl chloride
Cinnamyl chloride
Cinnamyl chloride
Cinnamyl chloride
Phenol
p-Cresol
Phenol
p-Cresol
Phenol
p-Cresol
Phenol
p-Cresol
Phenol
p-Cresol
Phenol
1a, 2a
1b, 2b
1a, 2a
1b, 2b
1a, 2a
1b, 2b
1a, 2a
1b, 2b
1a, 2a
1b, 2b
1a, 2a
1b, 2b
72
75
64
67
54
55
48
45
61
63
55
58
98/2
89/11
90/10
84/16
87/13
90/10
88/12
77/23
96/4
2
3
4
5
6
88/12
89/11
86/14
p-Cresol
a
Isolated yields of the combined regioisomers.
As determined by 1H NMR.
b
Mass spectroscopic analysis
tions. The results (Fig. 2) indicated that the formation of benzam-
ide increased initially with the progress of the reaction time,
reached a maximum and then remained unchanged. A reasonable
yield for the formation of benzamide was observed at the optimum
reaction time of 10 h (87%), whereas over a period of 16 h the max-
imum yield (90%) was achieved.
ESI-Mass spectral analyses of the new complexes were studied
in order to confirm molecular mass of the complexes. The m/z val-
ues of molecular ion peaks for the complexes [RuCl(CO)(PPh3)(L1)]
1, [RuCl(CO)(PPh3)(L2)] 2, [RuCl(CO)(Py)(L1)] 3, [RuCl(CO)(Py)(L2)]
4, [RuCl(CO)(AsPh3)(L1)] 5 and [RuCl(CO)(AsPh3)(L2)] 6 were ob-
tained at 652.9, 714.9, 468.1, 530.1, 698.1 and 758.0 respectively.
The calculated molecular weights corresponds to these complexes
are 652.09, 714.17, 468.90, 530.97, 698.04 and 758.11. This
showed that the obtained molecular masses are in good agreement
with that of the calculated molecular weights.
Further, the efficiency of all the six ruthenium(II) carbonyl com-
plexes towards the one-pot conversion of aldehydes to amides was
also investigated by optimized reaction conditions (Table 2). The
order of catalytic activity based on yield was 1 > 2 > 5 > 6 > 3 > 4.
In terms of substituent present in the Schiff base moiety and co-li-
gands, the order of activity is CH3 > C6H5 and PPh3 > AsPh3 > Py.
Hence, it was inferred that the electron donating/withdrawing
substituent plays a major role in deciding the catalytic activity of
their corresponding complexes. The presence of electron donat-
ing/withdrawing group in the substrate benzaldehyde derivatives
also alters yield of the products. Electron donating groups like
ACH3 and AOCH3 in the substrate have shown 80–66% and
78–60% yields respectively which is slightly lesser than that of
unsubstituted benzaldehyde (87–72%). On the other hand, substi-
tution of electron withdrawing groups like ANO2 and ACl in benz-
aldehyde exhibited higher yield (91–80% and 89–75%) than above
aldehydes.
On the basis of analytical and spectral data, the following octa-
hedral structure has been tentatively proposed for all the new
ruthenium(II) carbonyl quinoline based NNO-tridentate Schiff base
complexes (Fig. 1).
Catalytic activity towards aldehydes to amides conversion
The catalytic study towards the one-pot conversion of various
aldehydes to the corresponding amides in presence of NH2OHÁHCl
using ruthenium(II) carbonyl complexes as catalysts was investi-
gated. In order to systematically investigate the influence of time
and effect of catalyst loading, a proper model had to be established.
To study the effect of catalyst concentration on the reaction,
substrate to catalyst ratio was varied from total catalyst amount
0.005 mmol to 0.03 mmol (Table 1). A moderate yield was ob-
served even at very low catalyst loading of 0.0075 mmol (entry
3). The yield improved with increase in catalyst loading and
reached to the highest value of 91% with 0.03 mmol of catalyst (en-
try 6). The reaction proceeded with good yield (89%) when the cat-
alyst loading was 0.01 mmol (entry 4). Therefore the catalyst
loading 0.01 mmol was the best suitable for the catalytic conver-
sion of aldehydes to amides. The dependence of the product yield
on reaction time was also studied by analyzing the reaction
mixture at regular intervals of time under similar reaction condi-
Ruthenium(II) catalyzed o-allyl phenols formation
The reaction of allylic chloride with phenols in presence of
K2CO3 requires thermal activation. After prolonged heating, cin-
namyl chloride is selectively converted to its linear ether
PhCH = CHCH2OPh [57,58]. Whereas, opposite regioselectivity
was observed at room temperature with high yields when ruthe-
nium(II) complexes used as catalyst [52]. The present catalytic sys-
tems were evaluated for regioselective allylation, using cinnamyl
chloride as linear substrate in the presence of phenols acting as
nucleophile and K2CO3 as mineral base at room temperature in a
low catalyst loading with good yields. The results are reported in

R. Manikandan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 501–508
507
Ph
Cl
RuII
Ln
RuIV
Ln
Ph
ArOH
OAr
OAr
Ph
[RuII]
[RuII]
Ln
and
Ln
+
RuII
Ph
Ln
OAr
Ph
OAr
Ph
Fig. 3. A plausible mechanism for the ruthenium(II) carbonyl complex catalyzed formation of o-allylation of phenols.
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with very good regioselectivity up to 98/2. These values are very
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Conclusion
A simple and convenient route for the formation of ruthe-
nium(II) carbonyl complexes of general formula [RuCl(CO)(B)(L1–
2)] (B = PPh3, Asph3 or Py; L1–2 = Quinoline based ligands) has been
established. The catalytic ability of the complexes for the conver-
sion of aldehydes to amides has been studied and the conversions
were found to be good. The presence of electron donating groups
like ACH3 in catalysts have shown enhanced catalytic activity.
The complexes were also active catalysts for the synthesis of allyl
aryl ethers starting from cinnamyl chloride and phenols using
K2CO3 as base. This catalytic system favoured the formation of
branched allyl aryl ethers under mild conditions at room
temperature.
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Acknowledgement
We are thankful to the IISC Bangalore, STIC Cochin, SAIF Punjab
University, Chandigarh, India for providing instrumental facilities.
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