Ruthenium(II) carbonyl complexes with N-[di(alkyl/aryl)carbamothioyl] benzamide derivatives and triphenylphosphine as effective catalysts for oxidation of alcohols

Article abstract of DOI:10.1080/00958972.2010.548007

Ruthenium(II) complexes, [RuCl(L)(CO)(PPh₃)₂] {where L = N-[di(alkyl/aryl)carbamothioyl]benzamide derivatives}, are prepared from reaction between [RuHCl(CO)(PPh₃)₃] and N-[di(alkyl/aryl)carbamothioyl]benzamide derivatives in toluene and characterized by elemental analysis and spectral data (electronic, infrared, ¹H NMR, and ³¹P NMR). The combination of [RuCl(L)(CO)(PPh₃)₂] (0.01 mmol) and N-methylmorpholine-N- oxide (NMO) (3 mmol) is an active catalyst for the oxidation of primary, secondary, cyclic, allylic, aliphatic, and benzylic alcohols to their corresponding aldehydes and ketones at room temperature. The oxidation protocol is simple to operate and gives the corresponding carbonyl compounds good to excellent yields.

Full text of DOI:10.1080/00958972.2010.548007

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Ruthenium(II) carbonyl
complexes with N-[di(alkyl/
aryl)carbamothioyl]benzamide
derivatives and triphenylphosphine
as effective catalysts for oxidation of
alcohols
N. Gunasekaran a , N. Remya a , S. Radhakrishnan b & R.
Karvembu a
a Department of Chemistry, National Institute of Technology,
Tiruchirappalli 620 015, India
b Central Electrochemical Research Institute, Karaikudi 630 006,
India
Version of record first published: 10 Jan 2011.
To cite this article: N. Gunasekaran , N. Remya , S. Radhakrishnan & R. Karvembu (2011):
Ruthenium(II) carbonyl complexes with N-[di(alkyl/aryl)carbamothioyl]benzamide derivatives
and triphenylphosphine as effective catalysts for oxidation of alcohols, Journal of Coordination
Chemistry, 64:3, 491-501
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Journal of Coordination Chemistry
Vol. 64, No. 3, 10 February 2011, 491–501
Ruthenium(II) carbonyl complexes with N-[di(alkyl/aryl)
carbamothioyl]benzamide derivatives and triphenylphosphine
as effective catalysts for oxidation of alcohols
N. GUNASEKARANy, N. REMYAy, S. RADHAKRISHNANz and
R. KARVEMBU*y
yDepartment of Chemistry, National Institute of Technology, Tiruchirappalli 620 015, India
zCentral Electrochemical Research Institute, Karaikudi 630 006, India
(Received 26 August 2010; in final form 5 November 2010)
Ruthenium(II) complexes, [RuCl(L)(CO)(PPh3)2] {where L ¼ N-[di(alkyl/aryl)carbamothioyl]
benzamide derivatives}, are prepared from reaction between [RuHCl(CO)(PPh3)3] and
N-[di(alkyl/aryl)carbamothioyl]benzamide derivatives in toluene and characterized by elemen-
tal analysis and spectral data (electronic, infrared, 1H NMR, and 31P NMR). The combination
of [RuCl(L)(CO)(PPh3)2] (0.01 mmol) and N-methylmorpholine-N-oxide (NMO) (3 mmol) is an
active catalyst for the oxidation of primary, secondary, cyclic, allylic, aliphatic, and benzylic
alcohols to their corresponding aldehydes and ketones at room temperature. The oxidation
protocol is simple to operate and gives the corresponding carbonyl compounds good to
excellent yields.
Keywords: Ruthenium(II); Thiourea derivatives; Triphenylphosphine; Catalytic oxidation;
NMO
1. Introduction
Oxidation of primary and secondary alcohols into their corresponding aldehydes and
ketones is a very important transformation that is used in the manufacture of a wide
range of products [1–4]. Traditionally, such transformations have been performed with
stoichiometric quantities of inorganic oxidants such as chromium(VI) compounds. The
quest for effective catalytic systems that use clean and inexpensive oxidants, such as
molecular oxygen, hydrogen peroxide, NMO, tert-butylhydroperoxide, or TEMPO, for
converting alcohols to carbonyl products, remains an important challenge. Thiourea
derivatives are versatile ligands due to their coordination ability to a wide range of
metal centers as either neutral ligands [5], monoanions [6], or dianions [7, 8].
N-[Di(alkyl/aryl)carbamothioyl]benzamide derivatives readily coordinate with metal
ions through O, S donors [9–13] and these ligands can alter the catalytic property of
complexes due to steric and electronic properties provided by various substituents.
*Corresponding author. Email: karvembu@rediffmail.com
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2011 Taylor & Francis
DOI: 10.1080/00958972.2010.548007

492
N. Gunasekaran et al.
Recently we developed an active and selective ruthenium(III)–PPh3/NMO catalytic
system for the oxidation of primary and secondary alcohols to their corresponding
aldehydes and ketones [14]. This catalytic system did not give satisfactory results for the
oxidation of linear and cyclic aliphatic alcohols even at elevated temperature. In the
present work, ruthenium(II) carbonyl complexes containing N-[di(alkyl/aryl)carba-
mothioyl]benzamide derivatives and triphenylphosphine are improved and highly
efficient catalysts for the oxidation of various alcohols to carbonyl compounds in the
presence of NMO as oxidant at room temperature. The present catalytic system
exhibited high activity for the oxidation of linear and cyclic aliphatic alcohols. The
structures of the ligands used in this work are given in figure 1.
2. Experimental
2.1. Materials and methods
All solvents were dried and purified by standard methods. Infrared (IR) spectra were
recorded as KBr pellets with a Perkin-Elmer Spectrum RX1 FT-IR spectrophotometer
from 4000 to 400 cmꢀ1. Electronic spectra of the complexes were recorded in ethanol
solutions using a PG Instruments Ltd. T90þ spectrophotometer from 800 to 200 nm.
Magnetic susceptibility measurements were made with a Sherwood Scientific Auto
Magnetic Susceptibility Balance. Microanalyses were carried out with a Vario EL
1
AMX-400 elemental analyzer. H NMR and 31P NMR spectra were recorded with a
Bruker Avance 400 MHz instrument in CDCl3 using TMS and H3PO4 as internal
standards, respectively. Melting points were recorded with a Veego VMP-D melting
O
S
O
S
O
S
N
H
N
N
H
N
N
H
N
HL1
HL2
HL3
O
S
O
S
N
H
N
N
H
N
HL4
HL5
Figure 1. Structure of ligands.

Ruthenium(II) carbonyl complexes
493
point apparatus and were uncorrected. Capillary gas chromatography was performed
on a Shimadzu GC-2010 gas chromatograph.
2.2. Synthesis of Ru(II) complexes
All the complexes are prepared by the following general procedure. Ligand (HL)
(0.062–0.084 g, 0.26 mmol) dissolved in toluene (15 mL) was added to
[RuHCl(CO)(PPh3)3] (0.25 g, 0.26 mmol) in toluene (10 mL). The mixture was heated
in an oil bath at 80ꢁC. After 24 h, the reaction mixture was concentrated to 3 mL and
20 mL of n-hexane was added. The precipitate formed was filtered, recrystallized from
dichloromethane/n-hexane, and dried in vacuo.
[RuCl(L1)(CO)(PPh3)2] (1) is prepared from [RuHCl(CO)(PPh3)3] (0.25 g, 0.26 mmol)
and HL1 (0.081 g, 0.26 mmol). Yield: 88%, decomposition point 125ꢁC, Anal. Calcd for
C57H48ClN2O2P2RuS (%): C, 66.89; H, 4.73; N, 2.74; S, 3.13. Found (%): C, 66.29; H,
4.20; N, 2.50; S, 3.00. FT-IR (KBr, cmꢀ1): ꢀ(N–H) disappeared; ꢀ(
) 1485;
O
C
ꢀ(
) 1187; ꢀ(CꢂO) 1943; bands due to PPh 1435, 1093, 744. UV [ethanol, ꢁ in
(C S)
3
nm (" in dm3 molꢀ1 cmꢀ1)]: 226 (45,685), 271 (13,971), 414 (1771). 1H NMR (ppm): 6.6–
7.7 (m, 45H, aromatic). 31P NMR (ppm): 30.9 (s).
[RuCl(L2)(CO)(PPh3)2] (2) is prepared from [RuHCl(CO)(PPh3)3] (0.25 g, 0.26 mmol)
and HL2 (0.062 g, 0.26 mmol). Yield: 78%, decomposition point 105ꢁC, Anal. Calcd for
C55H60ClN2O2P2RuS (%): C, 65.30; H, 5.98; N, 2.77; S, 3.16. Found (%): C, 65.21; H,
5.90; N, 2.67; S, 3.07. FT-IR (KBr, cmꢀ1): ꢀ(N–H) disappeared; ꢀ(
) 1483;
C
O
ꢀ(
) 1190; ꢀ(CꢂO) 1935; bands due to PPh 1436, 1094, 747. UV [ethanol, ꢁ in nm
S
C
3
(" in dm3 molꢀ1 cmꢀ1)]: 226 (63,085), 265 (11,285). H NMR (ppm): 7.0–7.6 (m, 35H,
1
aromatic), 3.0–3.4 (q, 4H, methylene), 0.6–0.9 (t, 6H, methyl). 31P NMR (ppm): 31.4 (s).
[RuCl(L3)(CO)(PPh3)2] (3) is prepared from [RuHCl(CO)(PPh3)3] (0.25 g, 0.26 mmol)
and HL3 (0.069 g, 0.26 mmol). Yield: 80%, decomposition point 107ꢁC, Anal. Calcd for
C59H68ClN2O2P2RuS (%): C, 66.37; H, 6.42; N, 2.62; S, 3.00. Found (%): C, 66.29; H,
6.35; N, 2.56; S 2.93. FT-IR (KBr, cmꢀ1): ꢀ(N–H) disappeared; ꢀ(
) 1472;
C
O
ꢀ(
C
) 1187; ꢀ(CꢂO) 1954; bands due to PPh 1435, 1093, 743. UV [ethanol, ꢁ in
S
3
nm (" in dm3 molꢀ1 cmꢀ1)]: 225 (42,800), 275 (19,971), 410 (3142). 1H NMR (ppm): 7.5–
7.7 (m, 35H, aromatic), 3.0–3.3 (t, 4H, methylene), 2.9 (s, 8H, methylene), 0.7–1.0 (q,
6H, methyl). 31P NMR (ppm): 31.5 (s).
[RuCl(L4)(CO)(PPh3)2] (4) is prepared from [RuHCl(CO)(PPh3)3] (0.25 g, 0.26 mmol)
and HL4 (0.084 g, 0.26 mmol). Yield: 78%, decomposition point 102ꢁC, Anal. Calcd for
C59H52ClN2O2P2RuS (%): C, 67.39; H, 4.98; N, 2.66; S, 3.04. Found (%): C, 67.29; H,
4.89; N, 2.55; S, 2.97. FT-IR (KBr, cmꢀ1): ꢀ(N–H) disappeared; ꢀ(
) 1482;
C
O
ꢀ(
) 1190; ꢀ(CꢂO) 1962; bands due to PPh 1435, 1093, 746. UV [ethanol, ꢁ in nm
S
C
3
(" in dm3 molꢀ1 cmꢀ1)]: 226 (60,457), 271 (16,942). H NMR (ppm): 7.4–7.7 (m, 45H,
1
aromatic), 0.8–1.3 (m, 4H, methylene). 31P NMR (ppm): 29.5 (s).
[RuCl(L5)(CO)(PPh3)2] (5) is prepared from [RuHCl(CO)(PPh3)3] (0.25 g, 0.26 mmol)
and HL5 (0.077 g, 0.26 mmol). Yield: 88%, decomposition point 176ꢁC, Anal. Calcd for
C51H52ClN2O2P2RuS (%): C, 64.11; H, 5.49; N, 2.93; S, 3.36. Found (%): C, 68.70; H,
5.41; N, 2.85; S, 3.28. FT-IR (KBr, cmꢀ1): ꢀ(N–H) disappeared; ꢀ(
) 1481;
C
O
ꢀ(
C
) 1188; ꢀ(CꢂO) 1956; bands due to PPh 1435, 1093, 744. UV [ethanol,
S
3

494
N. Gunasekaran et al.
ꢁ in nm (" in dm3 molꢀ1 cmꢀ1)]: 227 (64,885), 271 (30,371), 406 (4570). 1H NMR (ppm):
7.3–7.7 (m, 35H, aromatic), 3.3–3.6 (s, 1H, methine), 1.4 (d, 6H, methyl). 31P NMR
(ppm): 29.5 (s).
2.3. Procedure for catalytic oxidation
To a solution of alcohol (1 mmol) in solvent (20 mL), N-methylmorpholine-N-oxide
(3 mmol) and the ruthenium complex (0.01 mmol) were added. The solution was stirred
for 12 h at room temperature. At the requisite time aliquots of the reaction mixture were
removed and the alcohol and aldehyde/ketone were extracted with n-hexane. The
n-hexane extract was then analyzed by GC.
3. Results and discussion
The bidentate ligands (HL1, HL2, HL3, HL4, and HL5) are synthesized from benzoyl
chloride, potassium thiocyanate, and the corresponding secondary amine [15]. New six-
coordinate ruthenium(II) carbonyl complexes, [RuCl(L)(CO)(PPh3)2], are synthesized
by reacting [RuHCl(CO)(PPh3)3] [16] with N-[di(alkyl/aryl)carbamothioyl]benzamide
derivatives (HL) (scheme 1). Spectral analysis revealed monoanionic bidentate
coordination of N-[di(alkyl/aryl)carbamothioyl]benzamide derivatives replacing one
triphenylphosphine and one hydride from the starting complex. All the complexes are
air stable, non-hygroscopic, insoluble in water and highly soluble in CH2Cl2, CH3CN,
C6H6, C2H5OH, DMF, and DMSO. The analytical data obtained are in good
agreement with the proposed molecular formulae.
3.1. IR spectroscopic analysis
In IR spectra of free carbamothioyl ligands, a very strong absorption band is at 3174–
3329 cmꢀ1 for N–H, which disappears on complexation with ruthenium, indicating
deprotonation of the ligands prior to coordination through enolization. The free ligands
exhibit a strong band corresponding to C ¼ O at 1652–1692 cmꢀ1. In complexes, this
band is at 1472–1485 cmꢀ1 indicating coordination of
to ruthenium. A medium
C
O
intensity band at 1243–1314 cmꢀ1 due to C ¼ S of the ligands undergoes a shift to lower
frequency (1187–1190 cmꢀ1) after complexation, revealing bonding through sulfur [15].
These complexes show new bands at 1410, 1100, and 750 cmꢀ1, which are due to
triphenylphosphine ligand. All the new complexes show a strong absorption band
around 1935–1962 cmꢀ1 due to terminally coordinated carbonyl [17].
3.2. Electronic spectroscopic analysis
All the new ruthenium complexes are diamagnetic (meff ¼ 0), indicating ruthenium in þ2
1
oxidation state. The ground state of ruthenium(II) is A1g arising from the t26g
configuration in an octahedral environment. The excited states corresponding to the
3
3
1
1
t52ge1g configuration are T1g, T2g, T1g, and T2g. Hence, four bands corresponding to

Ruthenium(II) carbonyl complexes
495
PPh3
O
S
Cl
2
Ru
N
N
CO
PPh3
Toluene,
80°C,
HL2
24 h
PPh3
Cl
Ru
PPh3
Cl
Ru
CO
PPh3
O
S
HL1
HL3
O
S
[RuHCl(CO)(PPh3)3]
N
N
N
N
Toluene,
80°C,
24 h
Toluene,
80°C,
24 h
CO
PPh3
Toluene,
80°C,
24 h
Toluene,
80°C,
HL4
HL5
24 h
3
1
PPh3
O
S
Cl
PPh3
Ru
N
N
O
Cl
CO
PPh3
Ru
CO
PPh3
N
S
N
4
5
Scheme 1. Formation of Ru(II) complexes.
3
1
3
1
1
1
1
1A1g ! T1g, A1g ! T2g, A1g ! T1g, and A1g ! T2g are possible in order of
increasing energy. Electronic spectra of all the complexes in ethanol showed two to
three bands in the region 414–225 nm. On the basis of high extinction coefficients
(" ¼ 11,285–64,885 molꢀ1 cmꢀ1 dm3), the bands appearing at 275–225 nm have been
assigned to charge transfer transitions arising from the excitation of an electron from
the metal t2g level to an unfilled molecular orbital derived from the ꢂ* level of the
ligands. The other bands around 414–406 nm have been assigned to the d–d transition
1
(1A1g ! T1g). The nature of electronic spectra are similar to those observed for other
octahedral ruthenium(II) complexes [18, 19].
3.3. NMR spectroscopic analysis
1H NMR spectra of all the complexes have been recorded in CDCl3 solution. All the
Ru(II) complexes exhibit a multiplet around 6.6–7.7 ppm, which has been assigned to
the protons of the phenyl groups present in triphenylphosphine and the ligand. The
characteristic signal at 11–12 ppm for N–H disappeared in NMR spectra of the
complexes indicating deprotonation of the ligands prior to coordination through
enolization [20]. Complex 2 exhibits a quartet at 3.0–3.4 ppm corresponding to
methylene and a triplet around 0.6–0.9 ppm corresponding to methyl. Complex 3

496
N. Gunasekaran et al.
Table 1. Optimization of catalytic oxidationa.
O
OH
[Ru] (0.01 equiv),
Oxidant (3 equiv), Solvent
Stirring, 27°C,12h
1 equiv
Entry
Complex
Solvent
Oxidant
Yield (%)b
1
2
3
4
5
6
7
8
9
1
2
3
4
5
5
5
5
5
5
5
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH3CN
C6H6
NMO
NMO
NMO
NMO
NMO
NMO
NMO
NMO
NMO
H2O2
94
95
94
92
97
98
93
97
98
94
97
DMF
CH3CN
CH3CN
CH3CN
10
11
t-BuOOH
aReaction conditions: 1-phenylethanol (1 mmol), oxidant (3 mmol), catalyst
(0.01 mmol), solvent (20 mL), stirring for 12 h, 27ꢁC.
bYield is determined by GC with area normalization; GC conditions: RTX-5
column, 60 m ꢃ 0.32 mm, 250ꢁC; FID detector, 280ꢁC; injector, 250ꢁC; carrier gas:
N2; rate: 1.39 mL minꢀ1
.
exhibits a triplet around 3.0–3.3 ppm corresponding to methylene protons near nitrogen
and a broad signal around 2.9 ppm attributed to remaining methylene protons of the
aliphatic carbon chain. Two triplets at 0.7–1.0 ppm in 3 have been assigned to methyls.
Complex 4 exhibits two multiplets at 0.8–1.3 ppm corresponding to methylene protons
attached to phenyl. In 5, two doublets at 1.2–1.4 ppm are due to methyls and two broad
singlets at 3.3 and 3.6 ppm are from methine protons attached to nitrogen. 31P NMR
spectra of all the complexes in CDCl3 confirm the presence of triphenylphosphine in
Ru(II) complexes. All complexes exhibit one signal at 29.5–31.5 ppm, indicating that
both phosphorus atoms are magnetically equivalent and hence, trans triphenylpho-
sphines were assigned [21, 22].
3.4. Catalytic oxidation
In order to explore the catalytic activity of ruthenium(II) complexes, 1–5 were tested as
catalysts for the oxidation of 1-phenylethanol (table 1, entries 1, 2, 3, 4, and 5) in the
presence of NMO as oxidant and dichloromethane as solvent at 27ꢁC. Although all the
complexes exhibit good catalytic activity, the yield of acetophenone (table 1, entry 5)
was highest when 5 was used as a catalyst. Hence, 5 was chosen as catalyst for
optimization and extending the scope of substrates. In no case was there detectable
oxidation of alcohols in the presence of NMO alone [23]. The catalytic oxidation of
1-phenylethanol (table 1, entries 5, 6, 7, and 8) was carried out in dichloromethane,
acetonitrile, benzene, and dimethylformamide in order to optimize the solvent.
Among these, acetonitrile (table 1, entry 6) was a better solvent as the yield
of carbonyl compound was 98%. The catalytic oxidation of 1-phenylethanol

Ruthenium(II) carbonyl complexes
Table 2. Oxidation of alcohols by 5a.
497
[Ru] (0.01 equiv),
OH
R2
O
Oxidant (3 equiv), CH3CN
R1
R1
R2
Stirring, 27°C, 12h
1 equiv
Entry
1
Substrate
Product
Yield (%)b
98 (94)c
OH
O
OH
O
2
3
4
99 (95)c
OH
O
97
OH
O
98
Cl
Cl
Cl
Cl
O
OH
5
6
7
94
88
94
OH
O
O
O
O
OH
H
O
OH
8
94
H
(continued )

498
N. Gunasekaran et al.
Table 2. Continued.
Entry
Substrate
Product
Yield (%)b
OH
O
9
94
OH
O
10
96
OH
O
11
12
95
93
OH
O
OH
O
13
98
aReaction conditions: alcohol (1 mmol), NMO (3 mmol), catalyst (0.01 mmol), acetonitrile (20 mL), stirring for 12 h, 27ꢁC.
bYield (average of two trials) is determined by GC with area normalization.
cIsolated yield is given in parenthesis.
(table 1, entries 9, 10, and 11) was carried out using NMO, hydrogen peroxide or tert-
butylhydroperoxide as oxidant in order to select the suitable oxidant for the present
catalyst. With NMO (table 1, entry 9), the yield of acetophenone was 98%; 0.01 mmol
of catalyst and 3 mmol of NMO were sufficient for oxidation. Acetonitrile was used as
solvent, NMO as oxidant, and 5 as catalyst for extending the scope of substrates.
Table 2 shows the results for the oxidation of various alcohols. Virtually every alcohol
investigated was converted to the corresponding carbonyl compound with ꢄ90% yield
at room temperature. The yield of carbonyl compounds obtained is significantly higher
than those obtained from recently reported Ru(III)-PPh3/NMO catalytic system [14].
Benzylic primary (table 2, entry 7) and secondary alcohols (table 2, entries 1, 2, 3, 4, and
5) are smoothly oxidized to the corresponding carbonyl compounds with excellent
yields. The efficiency of oxidation of benzylic alcohols is comparable with already
reported [Ru(PPh3)3Cl2]/hydroquinone/air [24] and [RuCl2(p-cymene)]2/Cs2CO3/O2 [25]
catalytic systems, and higher than Ru(III)-PPh3/NMO [26], Ru(II)-PPh3/NMO [27],
and [Ru(acac)2(CH3CN)2]PF6/H5IO6 [28] catalytic systems. The catalytic oxidation of
1-phenoxy-2-propanol (table 2, entry 6) gave corresponding ketone with 88% yield at
room temperature, whereas oxidation of the same substrate by similar Ru(III)
complexes with NMO gave the product with 75% yield after stirring for 12 h at 70ꢁC
[14]. The present catalytic system exhibits better efficiency for the oxidation of
cinnamylalcohol (table 2, entry 8) when compared with earlier reports on ruthenium

Ruthenium(II) carbonyl complexes
499
O
Ru(II)-PPh
3
O
+
N
H O
+
2
R
R
R
1
2
–
H C
O
3
O
N
OH
+PPh
3
R
1
2
Ru(IV)=O
CH
3
Scheme 2. Proposed mechanism for oxidation of alcohols.
complexes as catalysts and NMO/t-BuOOH as oxidant [29–31]. 1-Indanol (table 2,
entry 9) was readily converted into 1-indanone with 94% yield and the yield of product
is higher than K3[Fe(CN)6] or Shvo complex-catalyzed oxidation of the same substrate
with TEMPO or molecular oxygen, respectively [32, 33]. Oxidation of 1-cyclohex-
ylethanol (table 2, entry 10) was carried out at 27ꢁC to give corresponding ketone with
96% yield. Cyclohexanol (table 2, entry 11) and cyclopentanol (table 2, entry 12) are
converted into cyclohexanone (95% yield) and cyclopentanone (93% yield), respec-
tively. Oxidation of these substrates was found to be difficult due to the fact that ꢃ-CH
unit is less acidic than aromatic substrates [29]. Interestingly, the present catalytic
system is highly efficient for these substrates and yield of products is higher than those
obtained from [RuCl2(p-cymene)]2/Cs2CO3/O2 [25] and Ru-SiO2/t-BuOOH [34] cata-
lytic systems. Our catalyst is very active toward the oxidation of linear aliphatic alcohol
viz 2-octanol (table 2, entry 13) to 2-otanone (98% yield). The present catalytic system is
more efficient in the oxidation of linear aliphatic alcohols compared to Ru(II)/Ru(III)–
NMO catalytic systems [35–38]. It is found that cycloruthenated carbonyl complexes
[37] and Ru(II) half sandwich complexes [38] are equally efficient compared with our
system, but they require high temperature. The present catalytic system oxidizes 2-
octanol with excellent yield at room temperature. Recently, the catalytic oxidation of
alcohols by Ru(II) and Ru(III) complexes containing Schiff-base ligand and PPh3/
AsPh3 have been reported [39–41]. Compared to these systems, the present catalytic
system is better in terms of yield of products and mild reaction conditions.
A characteristic peak at 850 cmꢀ1 in the IR spectrum of reaction mixture supports the
fact that the catalytic cycle passes through a Ru(IV) ¼ O species [42]. The proposed
mechanism is given in scheme 2.
4. Conclusion
We have synthesized Ru(II) carbonyl complexes containing N-[di(alkyl/aryl)carba-
mothioyl]benzamide derivatives and triphenylphosphine. These complexes are
employed as catalysts in combination with NMO for oxidation of various alcohols at
room temperature. The catalytic procedure is simple and easy to implement.

500
N. Gunasekaran et al.
Supplementary material
Electronic spectra, representative 1H and 31P-NMR spectrum of ruthenium(II)
complexes, GC chromatogram, and GC conditions for catalytic studies have been
provided as supplementary materials.
Acknowledgments
Gunasekaran thanks NITT for fellowship. Karvembu acknowledges DST, Government
of India, for financial assistance under SERC Fast Track scheme for Young Scientists
(No. SR/FTP/CS-80/2006).
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