Ruthenium(II) 8-quinolinolates: Synthesis, characterization, crystal structure and catalysis in the synthesis of 2-oxazolines

Article abstract of DOI:10.1016/j.jorganchem.2015.06.005

Abstract New octahedral ruthenium(II) complexes (1-4) have been synthesized from the reaction of ruthenium(II) precursors [RuHCl(CO)(EPh₃)₃] (E = P or As) with the bidentate Schiff base ligands, 2-((2,6-dimethylphenylimino)methyl)quinolin-8-ol (L₁) and 2-((2,6-diisopropylphenylimino)methyl)quinolin-8-ol (L₂) in ethanol. These complexes have been characterized by elemental analyses, IR, UV-Vis, ¹H, ¹³C and ³¹P NMR and ESI-Mass spectroscopy. The molecular structure of the complex [RuCl(CO)(PPh₃)₂(L₂)] (2) was determined by single-crystal X-ray diffraction, which reveals a distorted octahedral geometry around ruthenium(II) ion. The catalytic activity of the new complexes was evaluated for the condensation of nitriles with ethanolamine under solvent free conditions. The processes were operative with aromatic and heteroaromatic nitriles and tolerated several substitutional groups. The studies on the effect of substitution over ligands, coligands, reaction time, temperature and catalyst loading were carried out in order to find the best catalyst in this series of complexes and favorable reaction conditions. A probable mechanism for the catalytic condensation of nitrile has also been proposed. The catalyst was recovered and recycled up to five times without significant loss of its activity.

Full text of DOI:10.1016/j.jorganchem.2015.06.005

Accepted Manuscript
Ruthenium(II) 8-quinolinolates: Synthesis, characterization, crystal structure and
catalysis in the synthesis of 2-oxazolines
P. Anitha, R. Manikandan, G. Prakash, B. Pachiyappan, P. Viswanathamurthi, J.G.
Malecki
PII:
S0022-328X(15)30032-2
10.1016/j.jorganchem.2015.06.005
JOM 19107
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 16 April 2015
Revised Date: 1 June 2015
Accepted Date: 3 June 2015
Please cite this article as: P. Anitha, R. Manikandan, G. Prakash, B. Pachiyappan, P. Viswanathamurthi,
J.G. Malecki, Ruthenium(II) 8-quinolinolates: Synthesis, characterization, crystal structure and
catalysis in the synthesis of 2-oxazolines, Journal of Organometallic Chemistry (2015), doi: 10.1016/
j.jorganchem.2015.06.005.
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ACCEPTED MANUSCRIPT
R
N
CH
R
EPh3
N
O
CO
Cl
Ru
EPh3
O
N
H2N
OH
R
CN
+
R

ACCEPTED MANUSCRIPT
Ruthenium(II) 8-quinolinolates: Synthesis, characterization, crystal structure
and catalysis in the synthesis of 2-oxazolines
P. Anithaa, R. Manikandana,1, G. Prakasha, B. Pachiyappana, P. Viswanathamurthia,*, J.G.
Maleckib
aDepartment of Chemistry, Periyar University, Salem-636011, Tamil Nadu, India.
bDepartment of Crystallography, Silesian University, Szkolna 9, 40-006 Katowice, Poland.
Abstract
New octahedral ruthenium(II) complexes (1-4) have been synthesized from the reaction of
ruthenium(II) precursors [RuHCl(CO)(EPh3)3] (E = P or As) with the bidentate Schiff base
ligands,
2-((2,6-dimethylphenylimino)methyl)quinolin-8-ol
(L1)
and
2-((2,6-
diisopropylphenylimino)methyl)quinolin-8-ol (L2) in ethanol. These complexes have been
1
characterized by elemental analyses, IR, UV-Vis, H, 13C and 31P NMR and ESI-Mass
spectroscopy. The molecular structure of the complex [RuCl(CO)(PPh3)2(L2)] (2) was determined
by single-crystal X-ray diffraction, which reveals a distorted octahedral geometry around
ruthenium(II) ion. The catalytic activity of the new complexes was evaluated for the
condensation of nitriles with ethanolamine under solvent free conditions. The processes were
operative with aromatic and heteroaromatic nitriles and tolerated several substitutional groups.
The studies on the effect of substitution over ligands, coligands, reaction time, temperature and
catalyst loading were carried out in order to find the best catalyst in this series of complexes and
favorable reaction conditions. A probable mechanism for the catalytic condensation of nitrile has
also been proposed. The catalyst was recovered and recycled up to five times without significant
loss of its activity.
Keywords:
Ru(II) carbonyl complexes
Crystal structure
2-Oxazolines
Recyclable catalyst
* Corresponding author. Fax: +91 427 2345124.
E-mail address: viswanathamurthi72@gmail.com (P. Viswanathamurthi).
1Present address: Department of Chemistry, KSR College of Arts and Science, Tiruchengode-
637 215, India.
1

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Introduction
Heterocyclic compounds are of great importance as pharmaceuticals, agrochemicals and
ligands for organometallic chemistry [1]. Among the various heterocycles, 2-oxazoline has
drawn tremendous attention due to their extensive applications in chemistry, biochemistry and
pharmacology [2-5]. This heterocycle is found in the structure of many biologically active
natural products [6]. It is also known as important intermediates in organic transformations [7].
Therefore, a great deal of attention, in recent years, has been devoted to the development of
efficient methodologies for the preparation of such compounds. A number of methods have been
developed for the preparation of 2-oxazolines from carboxylic acids [8], carboxylic esters [9],
nitriles [10,11], aldehydes [12], hydroxyamides [13] and olefins [14]. Although these methods
are valuable, most of them involve one or more disadvantages including harsh reaction
conditions, long reaction times, low yields of products, use of stoichiometric amounts of
catalysts, use of excess amounts of reagents and relatively expensive reagents and/or toxic
solvents. So, the development of an efficient, simple and environmentally benign catalytic
procedure for synthesis of the heterocycles is still in high demand.
There has been considerable interest in the chemistry of transition metal complexes of
Schiff bases [15-18], as these ligands offer opportunities for inducing substrate chirality, tuning
the metal-centered electronic factor and enhancing the solubility and stability of either
homogeneous or heterogeneous catalysts [19-22]. Among the various Schiff bases, the
coordination compounds of 8-hydroxyquinoline are well known due to their applications
particularly in OLED (organic light emitting diode) materials [23,24]. But the study on catalytic
behavior of such species is rather limited. It is well known that a small variation in the
environment around Schiff base ligand affect its structure, chelate ring size and significantly
properties of the complexes. By introducing appropriate substituents, one could in principle, fine
tune the electronic structure, suitably to design a desired compound. A feasible approach in this
work is to extend the degree of π-conjugation in 8-hydroxyquinoline molecule.
On the other hand, among the transition metals, the ruthenium complexes have received
considerable attention due to their reactivity and efficiency as catalysts in wide spectrum of
reactions [25-30]. Stimulated by the success of both Schiff bases and ruthenium complexes in
catalytic activity, we have combined both types to prepare two new classes of hydroxyquinoline-
Schiff base ligands and their ruthenium complexes.
2

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So, based on the above facts and our continuous efforts in developing efficient transition
metal catalysts [31], herein, we have reported the synthesis, spectral characterization and crystal
structure of ruthenium(II) complexes containing substituted 8-hydroxyquinolinolate ligands with
triphenyl phosphine/arsine and carbonyl as co-ligands. In addition, the catalytic performance of
the ruthenium(II) complexes was studied towards the condensation of nitriles with ethanolamine
under solvent-free conditions to generate various 2-oxazolines.
Experimental
Materials and methods
All the reagents used were chemically pure and AR grade. The solvents were purified and
dried according to standard procedures. The ligands and the starting complexes
[RuHCl(CO)(PPh3)3], [RuHCl(CO)(AsPh3)3] were prepared according to literature procedures
[32-34]. Microanalyses of carbon, hydrogen and nitrogen were carried out using Vario EL III
Elemental analyzer at SAIF - Cochin India. The IR spectra of the ligand and their complexes
were recorded as KBr pellets on a Nicolet Avatar model spectrophotometer in 4000-400 cm-1
range. Electronic spectra of the ligand and their complexes have been obtained in
1
dichloromethane using a Shimadzu UV - 1650 PC spectrophotometer in 800-200 nm range. H,
31
13C and P NMR spectra were measured in Jeol GSX - 400 instrument using DMSO-d6 as the
1
solvent at room temperature. H, 13C and 31P NMR spectra were obtained using TMS and o-
phosphoric acid as the reference respectively. The ESI-MS spectra were performed by LC-MS
Q-ToF Micro Analyzer (Shimadzu) in the SAIF, Panjab University, Chandigarh. Melting points
were checked on a Technico micro heating table and were uncorrected.
Preparation of ligands (HL1, HL2)
2-Formyl-8-hydroxyquinoline (1 mM) was dissolved in dried and degassed ethanol (10
mL) and treated with ethanolic (10 mL) solution of 2,6-dimethylaniline/2,6-diisopropylaniline
(1 mM) in 1:1 molar ratio. A drop of acetic acid was added and the reaction mixture was
subsequently refluxed for 4 h. On cooling to room temperature, the yellow product obtained was
purified by column chromatography using dichloromethane and petroleumether (1:3) solvent
mixture.
3

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2-((2,6-dimethylphenylimino)methyl)quinolin-8-ol (HL1)
Yield: 85%; MP: 252 °C; Anal. calc. for C18H16N2O (%): C, 78.24; H, 5.84; N, 10.14. Found
(%): C, 78.36; H, 5.78; N, 10.25. IR (KBr, cm-1): 3372 (phenolic O-H), 1641 (azomethine CH=N),
1627 (ring C=N), 1324 (phenolic C-O). UV-Vis (λmax, nm): 355, 305. 1H NMR (DMSO-d6, ppm):
9.32 (s, phenolic O-H), 8.48 (s, azomethine CH=N), 7.69 (d, 1H, quin-H), 7.64 (d, 1H, quin-H),
7.40 (t, 1H, quin-H), 7.36 (d, 1H, quin-H), 7.27 (d, 1H, quin-H), 6.90 (d, 2H, Ar-H), 6.81 (d, 1H,
Ar-H), 2.28 (s, 6H, CH3).
2-((2,6-diisopropylphenylimino)methyl)quinolin-8-ol (HL2)
Yield: 88%; MP: 238 °C; Anal. calc. for C22H24N2O (%): C, 79.48; H, 7.28; N, 8.43. Found
(%): C, 79.36; H, 7.47; N, 8.25. IR (KBr, cm-1): 3470 (phenolic O-H), 1636 (azomethine CH=N), 1632
(ring C=N), 1326 (phenolic C-O). UV-Vis (λmax, nm): 359, 304. 1H NMR (DMSO-d6, ppm): 9.02
(s, phenolic O-H), 8.35 (s, azomethine CH=N), 7.72 (d, 1H, quin-H), 7.69 (d, 1H, quin-H), 7.44
(t, 1H, quin-H), 7.41 (d, 1H, quin-H), 7.38 (d, 1H, quin-H), 7.01 (d, 2H, Ar-H), 6.98 (d, 1H, Ar-
H), 3.68 (m, 2H, CH-iPr), 1.28 (d, 12H, CH3-iPr).
General procedure for the synthesis of new ruthenium(II) complexes (1-4)
To a solution of [RuHCl(CO)(EPh3)3] (E = P or As) (0.1 mM) in ethanol (20 mL), the
appropriate ligand (0.1 mM) was added in 1:1 molar ratio. The mixture was refluxed for 5 h in a
water bath, whereby the solution turned from pale yellow to red. After reducing the content to
half volume and standing for a day, the complex was obtained as a red precipitate. It was filtered
and washed several times with ether and dried under vacuum. Crystals suitable for X-ray
diffraction were obtained by slow evaporation of a concentrated solution of complex 2 in
ethanol.
[RuCl(CO)(PPh3)2(L1)] (1)
Yield: 84%; MP: 251 °C; Anal. calc. for C55H45ClN2O2P2Ru (%): C, 68.50; H, 4.70; N, 2.90.
Found (%): C, 68.39; H, 4.61; N, 2.78. IR (KBr, cm-1): 1932 (C≡O), 1639 (azomethine CH=N), 1584
(ring C=N), 1432 (phenolic C-O). UV-Vis (λmax, nm): 502, 362, 310. 1H NMR (DMSO-d6, ppm):
8.36 (s, azomethine CH=N), 7.88 (d, 1H, quin-H), 7.84 (d, 1H, quin-H), 7.53 (t, 1H, quin-H),
7.49 (d, 1H, quin-H), 7.45 (d, 1H, quin-H), 7.19 (d, 2H, Ar-H), 7.15 (d, 1H, Ar-H), 7.11-7.02 (m,
4

ACCEPTED MANUSCRIPT
30H, PPh3), 2.20 (s, 6H, CH3). 13C NMR (DMSO-d6, ppm): 202.80 (C≡O), 164.14 (phenolic C-
O), 152.13 (azomethine CH=N), 149.11 (quinoline ring C=N), 136.17, 135.81, 135.62, 134.47,
133.03, 132.15, 130.23, 128.70, 128.54, 127.35, 126.88, 126.39, 125.86, 124.38, 123.81 (Ar-C),
19.82 (CH3). 31P NMR (DMSO-d6, ppm): 30.22. ESI-Mass (m/z) = 928.7 [M-Cl]+.
[RuCl(CO)(PPh3)2(L2)] (2)
Yield: 81%; MP: 278 °C; Anal. calc. for C59H53ClN2O2P2Ru (%): C, 69.44; H, 5.23; N, 2.74.
Found (%): C, 69.56; H, 5.50; N, 2.86. IR (KBr, cm-1): 1942 (C≡O), 1633 (azomethine CH=N), 1590
(ring C=N), 1367 (phenolic C-O). UV-Vis (λmax, nm): 485, 374, 320. 1H NMR (DMSO-d6, ppm):
8.20 (s, azomethine CH=N), 7.91 (d, 1H, quin-H), 7.86 (d, 1H, quin-H), 7.50 (t, 1H, quin-H),
7.46 (d, 1H, quin-H), 7.41 (d, 1H, quin-H), 7.06 (d, 2H, Ar-H), 7.02 (d, 1H, Ar-H), 6.93-6.84 (m,
30H, AsPh3), 3.72 (m, 2H, CH-iPr), 1.29 (d, 12H, CH3-iPr). 13C NMR (DMSO-d6, ppm): 204.40
(C≡O), 163.17 (phenolic C-O), 152.34 (azomethine CH=N), 148.82 (quinoline ring C=N),
136.67, 136.21, 135.63, 135.32, 134.58, 133.71, 132.86, 131.40, 130.58, 129.96, 129.62, 128.77,
31
128.25, 127.60, 127.31 (Ar-C), 28.53 (CH-ipr), 22.92 (CH3-ipr). P NMR (DMSO-d6, ppm):
29.84. ESI-Mass (m/z) = 985.4 [M-Cl]+.
[RuCl(CO)(AsPh3)2(L1)] (3)
Yield: 84%; MP: 268 °C; Anal. calc. for C55H45ClN2O2As2Ru (%): C, 62.77; H, 4.31; N, 2.66.
Found (%): C, 62.54; H, 4.19; N, 2.52. IR (KBr, cm-1): 1948 (C≡O), 1640 (azomethine CH=N), 1578
(ring C=N), 1431 (phenolic C-O). UV-Vis (λmax, nm): 467, 365, 307. 1H NMR (DMSO-d6, ppm):
8.26 (s, azomethine CH=N), 7.96 (d, 1H, quin-H), 7.91 (d, 1H, quin-H), 7.52 (t, 1H, quin-H),
7.48 (d, 1H, quin-H), 7.44 (d, 1H, quin-H), 7.23 (d, 2H, Ar-H), 7.19 (d, 1H, Ar-H), 7.15-7.08 (m,
30H, AsPh3), 2.31 (s, 6H, CH3). 13C NMR (DMSO-d6, ppm): 203.41 (C≡O), 164.43 (phenolic C-
O), 152.77 (azomethine CH=N), 148.72 (quinoline ring C=N), 136.82, 136.53, 135.71, 135.26,
134.84, 134.40, 133.29, 132.75, 131.93, 131.17, 129.22, 128.58, 126.36, 125.82, 124.70 (Ar-C),
20.35 (CH3). ESI-Mass (m/z) = 1016.6 [M-Cl]+.
[RuCl(CO)(AsPh3)2(L2)] (4)
Yield: 81%; MP: 234 °C; Anal. calc. for C59H53ClN2O2As2Ru (%): C, 63.93; H, 4.82; N, 2.53.
Found (%): C, 63.70; H, 4.95; N, 2.39. IR (KBr, cm-1): 1938 (C≡O), 1634 (azomethine CH=N), 1580
5

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(ring C=N), 1403 (phenolic C-O). UV-Vis (λmax, nm): 474, 368, 304. 1H NMR (DMSO-d6, ppm):
8.18 (s, azomethine CH=N), 7.77 (d, 1H, quin-H), 7.74 (d, 1H, quin-H), 7.43 (t, 1H, quin-H),
7.40 (d, 1H, quin-H), 7.38 (d, 1H, quin-H), 7.22 (d, 2H, Ar-H), 7.18 (d, 1H, Ar-H), 7.15-7.07 (m,
30H, AsPh3), 3.78 (m, 2H, CH-iPr), 1.23 (d, 12H, CH3-iPr). 13C NMR (DMSO-d6, ppm): 203.56
(C≡O), 162.77 (phenolic C-O), 153.07 (azomethine CH=N), 149.21 (quinoline ring C=N),
137.16, 136.94, 135.68, 135.40, 134.97, 133.46, 133.19, 132.62, 131.30, 130.68, 129.94, 129.26,
127.75, 127.12, 126.83 (Ar-C), 28.13 (CH-ipr), 23.07 (CH3-ipr). ESI-Mass (m/z) = 1072.5 [M-
Cl]+.
X-ray crystallographic study
Crystal of 2 was mounted on glass fibers and used for data collection. Crystal data were
collected at 295(2) 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 structure was solved by direct methods using the program
SHELXS. Refinement and all further calculations were carried out using SHELXL [35]. 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. Atomic scattering factors were incorporated in the computer
programs.
Condensation of nitriles with ethanolamine
Nitrile (1 mM), ethanolamine (3 mM) and ruthenium(II) complex (4 M%) were mixed
and stirred for 5 h at 90 °C. After completion of the reaction, the mixture was cooled to room
temperature, diluted with ethyl acetate (10 mL) and filtered. The solid material (catalyst) was
washed with ethyl acetate, dried and then reused in the next run. The filtrate was concentrated
and the resulting residue was purified by column chromatography on silica gel using petroleum
ether/ethyl acetate (50:50) as eluent, to afford the desired product. The products were
characterized by 1H NMR [36].
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2-Phenyl-4,5-dihydrooxazole. 1H NMR (DMSO-d6, ppm): 7.19-7.96 (m, 5H, aromatic CH), 4.40-
4.51 (t, 2H, CH2), 3.71-3.82 (t, 2H, CH2).
1
2-(4-Nitrophenyl)-4,5-dihydrooxazole. H NMR (DMSO-d6, ppm): 8.36-8.40 (d, 2H, aromatic
CH), 8.09-8.12 (d, 2H, aromatic CH), 4.48-4.54 (t, 2H, CH2), 4.31-4.38 (t, 2H, CH2).
1
2-(4-Chlorophenyl)-4,5-dihydrooxazole. H NMR (DMSO-d6, ppm): 7.62-7.78 (d, 2H, aromatic
CH), 6.66-6.81 (d, 2H, aromatic CH), 4.41-4.48 (t, 2H, CH2), 4.02-4.10 (t, 2H, CH2).
2-(4-Acetylphenyl)-4,5-dihydrooxazole. 1H NMR (DMSO-d6, ppm): 8.24-8.32 (d, 2H, aromatic
CH), 7.92-8.01 (d, 2H, aromatic CH), 4.42-4.48 (t, 2H, CH2), 4.23-4.29 (t, 2H, CH2), 2.70 (s, 3H,
COCH3).
2-(4-Formylphenyl)-4,5-dihydrooxazole. 1H NMR (DMSO-d6, ppm): 8.28-8.36 (d, 2H, aromatic
CH), 8.02-8.09 (d, 2H, aromatic CH), 4.33-4.38 (t, 2H, CH2), 4.17-4.22 (t, 2H, CH2), 10.04 (s,
1H, CHO).
4-(4,5-Dihydrooxazol-2-yl)benzoicacid. 1H NMR (DMSO-d6, ppm): 8.26-8.37 (d, 2H, aromatic
CH), 8.15-8.23 (d, 2H, aromatic CH), 4.38-4.45 (t, 2H, CH2), 4.21-4.29 (t, 2H, CH2), 10.92 (s,
1H, COOH).
1
2-(4-methylphenyl)-4,5-dihydrooxazole. H NMR (DMSO-d6, ppm): 7.68-7.74 (d, 2H, aromatic
CH), 7.14-7.21 (d, 2H, aromatic CH), 4.51-4.68 (t, 2H, CH2), 4.12-4.19 (t, 2H, CH2), 2.41 (s, 3H,
CH3).
1
2-(4-Methoxyphenyl)-4,5-dihydrooxazole. H NMR (DMSO-d6, ppm): 8.38-8.50 (d, 2H, aromatic
CH), 8.02-8.14 (d, 2H, aromatic CH), 4.70-4.88 (t, 2H, CH2), 4.36-4.44 (t, 2H, CH2), 4.08 (s, 3H,
OCH3).
4-(4,5-Dihydrooxazol-2-yl)aniline. 1H NMR (DMSO-d6, ppm): 7.02-7.18 (d, 2H, aromatic CH),
6.88-6.92 (d, 2H, aromatic CH), 4.41-4.52 (t, 2H, CH2), 4.10-4.21 (t, 2H, CH2), 3.80 (s, 2H,
NH2).
1
2-(4-Hydroxyphenyl)-4,5-dihydrooxazole. H NMR (DMSO-d6, ppm): 7.10-7.22 (d, 2H, aromatic
CH), 6.74-6.85 (d, 2H, aromatic CH), 4.40-4.48 (t, 2H, CH2), 4.16-4.25 (t, 2H, CH2), 10.30 (s,
1H, OH).
2-(Naphthalen-2-yl)-4,5-dihydrooxazole. 1H NMR (DMSO-d6, ppm): 7.33-7.92 (m, 7H, aromatic
CH), 4.46-4.53 (t, 2H, CH2), 4.18-4.24 (t, 2H, CH2).
2-(Pyridin-4-yl)-4,5-dihydrooxazole. 1H NMR (DMSO-d6, ppm): 8.56-8.82 (d, 2H, aromatic CH),
8.08-8.18 (d, 2H, aromatic CH), 4.54-4.72 (t, 2H, CH2), 4.18-4.29 (t, 2H, CH2).
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2-(Thiophen-2-yl)-4,5-dihydrooxazole. 1H NMR (DMSO-d6, ppm): 7.53-7.81 (m, 3H, aromatic
CH), 4.28-4.35 (t, 2H, CH2), 4.02-4.09 (t, 2H, CH2).
2-(4,5-Dihydrooxazol-2-yl)aniline. 1H NMR (DMSO-d6, ppm): 7.28-7.42 (m, 4H, aromatic CH),
4.38-4.43 (t, 2H, CH2), 4.04-4.12 (t, 2H, CH2), 3.83 (s, 2H, NH2).
1
2-(2-Methylphenyl)-4,5-dihydrooxazole. H NMR (DMSO-d6, ppm): 7.32-7.70 (m, 4H, aromatic
CH), 4.42-4.50 (t, 2H, CH2), 4.06-4.14 (t, 2H, CH2), 2.39 (s, 3H, CH3).
1
2-(2-Chlorophenyl)-4,5-dihydrooxazole. H NMR (DMSO-d6, ppm): 7.31-7.64 (m, 4H, aromatic
CH), 4.53-4.60 (t, 2H, CH2), 4.21-4.30 (t, 2H, CH2).
Results and discussion
The quinolinolate ligands (HL1,2) were expected to act as tridentate NNO donors when it
treated with [RuHCl(CO)(EPh3)3] (E = P or As) in 1:1 molar ratio (Scheme 1) (product 1).
Unexpectedly, the quinolinolate ligands involved in this work deceived our expectations and
formed stable six coordinated metal complexes in which they act as bidentate NO donors
(product 2). The isolated complexes were stable at room temperature, non-hygroscopic in nature
and highly soluble in common organic solvents such as dichloromethane, chloroform, benzene,
acetonitrile, ethanol, methanol, dimethylformamide and dimethylsulfoxide. All the complexes
were structurally characterized by elemental analyses, IR, electronic, NMR and ESI-Mass
spectra. For further confirmation, the structure of complex 2 was elucidated by X-ray
crystallographic analysis.
Spectroscopic studies
The IR spectra of free ligands were compared with that of new complexes in order to
1
confirm the coordination of ligands to ruthenium metal. The band at 1632-1641 cmꢀ in the free
ligands can be assigned to azomethine, which remains unaltered in the complexes. This suggests
that the non-participation of azomethine group in bonding. In the spectra of free ligands, a strong
band was observed at the region 1627-1636 cm-1 which is characteristics of the C=N group of
quinoline ring and this band has been shifted to lower frequency (1578-1590 cm-1) in complexes
indicating the participation of quinoline nitrogen in bonding with ruthenium atom [37]. A strong
band appeared around the region 1324-1326 cm-1 in free ligands was assigned to the phenolic C-
O stretching which has been shifted to higher frequency (1367-1432 cm-1) in the complexes,
8

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showing that the other coordination is through the phenolic oxygen atom [38]. This has been
further confirmed by the disappearance of the broad O-H band around 3372-3470 cm-1 in all the
complexes due to the binding of phenolic –OH group to ruthenium after deprotonation [39]. The
strong absorption band around 1932-1948 cm-1 was due to the terminally coordinated carbonyl
group. In addition, the other characteristic absorption due to triphenylphosphine or
triphenylarsine was present in the expected region [40]. The electronic spectra of ligands and the
complexes have shown two to three bands in dichloromethane solvent. The bands obtained in the
region 304-374 nm in both the ligands and the complexes can be attributed to the intra-ligand
electronic transitions such as n→π* and π→π* of free azometine group. The band in the region of
467-502 nm can be assigned to charge transfer transition from t2g orbital of metal to the unfilled
π* molecular orbital of ligand [41-44].
1
The H NMR spectra of the ligands and their complexes showed the signals in the
expected regions. The spectra of free ligands exhibited a peak in the region 9.02-9.32 ppm which
is characteristic of phenolic O-H group. This peak was disappeared in their corresponding
complexes which confirmed that the binding of ligand with metal ion via deprotonation of
phenolic hydroxyl group. The ligands and their complexes exhibited a peak in the region of 8.18-
8.48 ppm was due to azomethine proton. The ligand L1 and their corresponding complexes
showed singlet in the region 2.20-2.28 ppm was assigned to methyl group protons attached to
benzene ring. The ligand L2 and their corresponding complexes showed doublet in the region
2.20-2.28 ppm and multiplet in the region 3.68-3.78 ppm were assigned to methyl and methine
protons of isopropyl group which are attached to benzene ring. Further, the spectra of ligands
and all the complexes showed a multiplet for aromatic protons at 6.81-7.96 ppm.
The 13C NMR spectra of all the complexes showed a sharp peak at 202.80-204.40 ppm
region, which has been attributed to terminal C≡O carbon. The phenolic carbon (C-O) and
azomethine (CH=N) carbon have exhibited peaks at 162.77-164.43 and 152.13-153.07 ppm
regions respectively. One sharp peak at 148.72-149.21 ppm region was correspond to C=N group
of quinoline ring. A sharp singlet at 19.82 and 20.35 ppm was observed in the spectra of
complexes 1 and 3 respectively, have been assigned to methyl carbon. A peak around 22.92-
23.01 and 28.13-28.53 ppm region was observed for complexes 2 and 4 respectively and these
9

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peaks were due to methyl and methine carbon of isopropyl group. In addition, all the aromatic
carbon atoms exhibited their corresponding peaks in the region 123.81-137.16 ppm as expected.
31P NMR spectra of complexes 1 and 2 were recorded to confirm the presence of
triphenylphosphine group and its geometry in the complexes. One sharp singlet at 30.22 and
29.84 ppm was observed for complexes 1 and 2 respectively which confirmed the trans
triphenylphospine geometry in both the complexes due to their symmetrical and chemically
identical nature.
ESI-Mass spectra of the complexes (1-4) show the molecular ion peak with the loss of a
chloride ion at m/z = 928.7, 985.4, 1016.6 and 1072.5. The calculated molecular mass correspond
to these complexes was 928.9, 985.0, 1016.8 and 1072.9. The obtained molecular mass of
complexes was in good agreement with that of the calculated molecular masses.
X-ray crystallography
Single crystal of 2 was obtained by the slow evaporation of ethanolic solution of
compound at room temperature. A red crystal of approximate dimensions 0.44
× 0.14 × 0.12 mm
was isolated and the single crystal X-ray diffraction experiment was carried out at 295 K. From
the unit cell dimensions, it was clear that the crystal was triclinic belonging to the P-1 space
group. Ellipsoidal plot of complex 2 labeled with atom numbering scheme was shown in Fig. 1.
The crystal data and structure refinement parameters of complex 2 was summarized in Table 1
and selected bond lengths and bond angles are depicted in Table 2. The ruthenium(II) ion
exhibits a hexa coordination with an octahedral geometry, where equatorial coordination comes
from ring nitrogen and phenolic oxygen of bidentate chelating ligand, a chloride and a carbonyl
carbon. A pair of triphenylphosphines completes the axial coordination. Though the PPh3 ligands
usually prefer to occupy mutually cis position for better π -interaction [45], but in this complex
the presence of CO, a stronger π-acidic ligand, might have forced the bulky PPh3 ligands to take
trans position for steric reasons. The +2 oxidation state of the complex is compensated by
chloride ion and deprotonated phenolic oxygen. The N(1)-Ru(1)-Cl(1) and O(2)-Ru(1)-C1(1)
bond angle is 168.40(9)° and 176.81(14)° respectively showing that Cl atom lies trans to ring
nitrogen and carbonyl lies trans to phenolic oxygen atom. The cis angles N(1)-Ru(1)-O(2) =
79.74(10)°, Cl(1)-Ru(1)-O(2) = 88.77(7)°, Cl(1)-Ru(1)-C(1) = 88.92(13)°, Cl(1)-Ru(1)-P(1) =
89.79(3)°, Cl(1)-Ru(1)-P(2) = 87.46(3)°, O(2)-Ru(1)-P(1) = 87.59(7)° and O(2)-Ru(1)-P(2) =
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88.86(7)° are acute, whereas the other cis angles N(1)-Ru(1)-C(1) = 102.62(15)°, P(1)-Ru(1)-
C(1) = 90.21(13)°, P(2)-Ru(1)C(1) = 93.24(13)°, P(1)-Ru(1)-N(1) = 91.29(8)° and P(2)-Ru(1)-
N(1) = 90.71(8)° are obtuse. The trans angles N(1)-Ru(1)-Cl(1) = 168.40(9)°, P(2)-Ru-P(1) =
175.55(4)° and O(2)-Ru(1)-C(1) = 176.81(14)° deviate from linearity. The variations in bond
angles lead to a significant distortion from an ideal octahedral geometry for the complex. The
Ru(1)-C(1), Ru(1)-Cl(1) Ru(1)−P(1) and Ru(1)−P(2) distances are 1.830(4), 2.4089(9),
2.4037(10) and 2.4108(10) Å. The observed bond distances are comparable with those found in
other reported ruthenium complexes containing PPh3 [46].
Synthesis of 2-oxazolines
Optimization of reaction conditions
Benzonitrile and ethanolamine were chosen as model substrates using complex 1 as
catalyst to optimize the reaction conditions including reaction time, temperature, catalyst loading
and the ratio of benzonitrile to ethanolamine (Table 3). The first set of reactions were run at
constant concentration of catalyst at various time intervals at 70 °C using 1:2 molar ratio of
benzonitrile and ethanolamine (entries 1-6). The yield increased with reaction time and total
reaction time of 5 h gave a constant conversion of 39%. Next, we focused on the effect of
reaction temperature on the catalyst activity (entries 7-12). The highest yield of 2-oxazoline was
obtained at 90 °C. Further, the reaction was carried out at different concentration of catalyst
(entries 13-16). A good yield was obtained for 4 M% of catalyst. It is noteworthy that the
reaction was not able to proceed smoothly without the use of a catalyst, giving only 8% yield
(Entry 17). Finally, to optimize the molar ratio of substrates, several ratios (1 : 1 to 1 : 5) were
employed. As shown in Table 3, the ratio of benzonitrile to ethanolamine imposed important
effects on the yield of 2-phenyloxazoline. The yield of product was gradually increased from 46
to 87% as the ratio of benzonitrile to ethanolamine was raised from 1 : 1 to 1 : 3 (entries 18-21).
In addition, we observed that the newly synthesized complex containing bidentate ligand
exhibited higher catalytic activity than that of pure ligand and the precursor complex (entries
22,23).
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Selection of favorable catalyst
In order to choose the best catalyst among the synthesized complexes, the condensation
reaction of benzonitrile with ethanolamine was carried out using the catalysts 1, 2, 3 and 4 under
the above optimized conditions (Table 4). The results showed that the complexes bearing
triphenylphospine (1 and 2) showed better activity compared to the rest of complexes (3 and 4)
due to the higher leaving property of triphenylphospine. In addition, the effect of substituent has
also slightly responsible for the catalytic activity. The complexes with methyl substituent
exhibited good activity than isopropyl substituent. It may due to the steric hindrance of bulkier
isopropyl substituent. Therefore, collectively, the complex that bearing both triphenylphospine
coligands and methyl substituent (complex 1) showed higher catalytic activity up to 87 % and so
it has been chosen as the favorable catalyst.
Condensation of various nitriles with ethanolamine
Upon the above optimization, the optimal reaction conditions were identified as follows:
solvent-free, 1 : 3 molar ratio of nitrile to ethanolamine, 4 M% of catalyst with a reaction time of
5 h at 90 °C. With the optimized reaction conditions in hand, a great number of nitrile substrates
were tested by combining with standard amino alcohol and it was observed that various
substitutions on the aromatic ring were allowed (Table 5). For example, electron-withdrawing
group (nitro, chloro, acetyl, formyl or carboxyl) substituted benzonitriles (entries 2-6) displayed
better performance with excellent yields 90-97%. On the other hand, the presence of an electron
donating group (methyl, methoxyl, amino or hydroxyl) in the ring of the benzonitriles gave
similar yields 81-87% (entries 7-10) as for unsubstituted benzonitrile (entry 1). The reaction of
2-naphthonitrile performed significantly well to give good yield (entry 11). Heteroaromatic
compounds such as isonicotinonitrile and thiophene-2-carbonitrile reacted with ethanolamine to
give better yields (entries 12,13). The reaction of aryl nitrile bearing ortho substituents gave
moderate yields as a result of steric hindrance (entries 14-16). In comparison with other reported
catalytic systems, our catalysts have been found to exhibit the best activity in terms of low
catalyst loading [47-49], low reaction time [50-53] and high yield without any side products
[53,54]. Moreover, the present catalytic system works under solvent-free conditions and prevent
the problems which many associate with use of solvent such as cost, handling, safety and
pollution.
12

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Catalyst recycling
Recovery and reusability of catalyst is an important theme in catalysis. This means the
catalyst can be used in many catalytic cycles and thereby more commercial for industrial
catalysis. For this purpose, the reaction of benzonitrile with ethanolamine was chosen as a model
reaction in the presence of 4 M% of complex 1 as catalyst. At the end of reaction, catalyst was
recovered from the reaction mixture by dilution of the mixture with ethyl acetate and filtered.
The catalyst was washed with ethyl acetate, dried and then reused in the next run. More than
90% of catalyst from the quantity initially used could be regenerated in its pure form using this
method. The isolated catalyst was reused up to five times without significant loss of its activity.
The filtrate was concentrated and the residue was purified by silica gel chromatography to afford
the pure 2-oxazoline.
Possible mechanism
The possible catalytic reaction mechanism [55] for the above reactions is proposed as
follows (Scheme 2). Firstly, the nitrile molecule replaces the PPh3 group and binds to the Ru(II)
centre of complex, producing the intermediate I. Secondly, the intermediate I combines with
ethanolamine to give the intermediate II through the nucleophilic addition. In the next step the
intermediate II undergoes intramolecular cycloaddition to generate III. Then the intermediate III
eliminates the tandem reaction product that loses one equivalent of NH3, producing the 2-
oxazoline and thus furnishing the catalytic cycle.
Conclusion
New ruthenium(II) 8-hydroxyquinolinolate complexes incorporating carbonyl and
triphenylphosphine/arsine have been synthesized and characterized. X-ray diffraction study of
complex 2 confirms the ON coordination mode of the ligands and reveals a distorted octahedral
geometry around the ruthenium(II) ion. The new complexes act as excellent recyclable catalysts
for the synthesis of 2-oxazolines with good to excellent isolated yields. All these complexes were
screened for their catalytic activity in condensation reaction and the complex 1 has been found to
be the most active one. This method offers several advantages including short reaction time,
excellent yields, simple work-up, ease for separation and recyclability of the catalyst, as well as
the ability to tolerate a wide variety of substitutions in the nitriles and environmentally-benign
13

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reaction conditions. The reusability of this catalyst was high and can be reused up to five times
without significant decrease from its initial activity. These advantages, in general, highlight this
protocol as a useful and attractive methodology for the rapid synthesis of biologically active 2-
oxazolines.
Supplementary material
CCDC 1047556 contains the supplementary crystallographic data for the complex 2.
These data can be obtained free of charge via www.ccdc.cam.ac.uk/data request/cif.
14

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References
[1] (a) R. W. DeSimone, K. S. Currie, S. A. Mitchell, J. W. Darrow, D. A. Pippin, Comb.
Chem. High Throughput Screening 7 (2004) 473.
(b) L. Kollar, G. Keglevich, Chem. Rev. 110 (2010) 4257.
[2] T.G. Gant, A.I. Meyers, Tetrahedron 50 (1994) 2297.
[3] J.A. Frump, Chem. Rev. 71 (1971) 483.
[4] M.R. Grimmett, in: A.R. Katritzky, C.W. Rees, E.F.V. Scriven (Eds.), Comprehensive
Heterocyclic Chemistry, Pergamon, Oxford, 3 (1996).
[5] A.G. Gilman, L.S. Goodman, The Pharmacological Basis of Therapeutics, 10th edn,
McGraw-Hill, NY (2001).
[6] J.V. Greenhill, L. Lue, in: G.P. Ellis, D.K. Luscombe (Eds.), Progress in Medicinal
Chemistry, Elsevier, NY 3 (1993) 170.
[7] K. Puntener, M.D. Hellman, E. Kuester, L.S. Hegedus, J. Org. Chem. 65 (2000) 8301.
[8] A. Cwik, Z. Hell, A. Hegedus, Z. Finta, Z. Horvath, Tetrahedron Lett. 43 (2002) 3985.
[9] P. Zhou, J.E. Blubaum, C.T. Burns, N.R. Natale, Tetrahedron Lett. 38 (1997) 7019.
[10] D.S. Clarke, R. Wood, Synth. Commun. 26 (1996) 1335.
[11] I. Mohammadpoor-Baltork, A.R. Khosropour, S.F. Hojati, Synlett (2005) 2747.
[12] J.G. Badiang, J. Aube, J. Org. Chem. 61 (1996) 2484.
[13] E.J. Corey, K. Ishihara, Tetrahedron Lett. 33 (1992) 6807.
[14] S. Minakata, M. Nishimura, T. Takahashi, Y. Oderaotoshi, M. Komatsu, Tetrahedron
Lett. 42 (2001) 9019.
[15] (a) Y. Sunatsuki, Y. Motoda, N. Matsumoto, Coord. Chem. Rev. 226 (2002) 199.
(b) C.M. Che, J.S. Huang, Coord. Chem. Rev. 242 (2003) 27.
[16] (a) H. Khanmohammadi, S. Amani, H. Lang, T. Rueffer, Inorg. Chim. Acta 360 (2007)
579.
(b) P. DiBernardo, P.L. Zanonato, S. Tamburini, P.A. Vigato, Inorg. Chim. Acta 360
(2007) 1083.
[17] (a) R.T. Ruck, E.N. Jacobsen, J. Am. Chem. Soc. 124 (2002) 2882.
(b) S. Adsule, V. Barve, D. Chen, F. Ahmed, Q.P. Dou, S. Padhye, F.H. Sarkar, J. Med.
Chem. 49 (2006) 7242.
[18] (a) D.J. de Geest Andy Noble, B. Moubaraki, K.S. Murray, D.S. Larsen, S. Brooker,
15

ACCEPTED MANUSCRIPT
Dalton Trans. (2007) 467.
(b) U. Beckmann, S. Brooker, Coord. Chem. Rev. 222 (2003) 17.
(c) S. Brooker, Coord. Chem. Rev. 222 (2001) 33.
[19] B. De Clercq, F. Verpoort, Macromolecules 35 (2002) 894.
[20] T. Opstal, F. Verpoort, Angew. Chem. Int. Ed. 42 (2003) 2876.
[21] C. Carlini, S. Giaiacopi, F. Marchetti, C. Pinzino, A.M.R. Galleti, G. Sbrana,
Organometallics 25 (2006) 3659.
[22] S.N. Pal, S. Pal, Inorg. Chem. 40 (2001) 4807.
[23] J.-F. Moulin, M. Brinkmann, A. Thierry, J.-C. Wittmann, Adv. Mater. 14 (2002) 436.
[24] L.S. Sapochak, F.E. Benincasa, R.S. Schofield, J.L. Baker, K.K.C. Riccio, D. Fogarty,
H. Kohlmann, K.F. Ferris, P. Burrows, J. Am. Chem. Soc. 124 (2002) 6119.
[25] L. Salvi, A. Salvini, F. Micoli, C. Bianchini, W. Oberhauser, J. Organomet. Chem. 692
(2007) 1442.
[26] C. Po Lau, S. Man Ng, G. Jia, Z. Lin, Coord. Chem. Rev. 251 (2007) 2223.
[27] C. Jun Yue, Y. Liu, R. He, J. Mol. Catal. A 259 (2006) 17.
[28] F. Nipa Haque, A.J. Lough, R.H. Morris, Inorg. Chim. Acta 361 (2008) 3149.
[29] P. Buskens, D. Giunta, W. Leitner, Inorg. Chim. Acta 357 (2004) 1969.
[30] J. Bravo, J. Castro, S. Garcia-Fontana, M.C. Rodriguez-Martinez, G. Albertin, S.
Antoniutti, A. Manera, J. Organomet. Chem. 692 (2007) 5481.
[31] (a) N. Dharmaraj, P. Viswanathamurthi, P.K Suganthy, K Natarajan, Transition met.
Chem. 23 (1998) 129.
(b) R. Karvembu, R. Prabhakaran, K. Senthilkumar, P. Viswanathamurthi,
React. Kinet. Catal. Lett. 86 (2005) 211.
(c) R. Ramachandran, G. Prakash, S. Selvamurugan, P. Viswanathamurthi, J.G.
Malecki, V. Ramkumar, Dalton Trans. 43 (2014) 7889.
(d) R. Manikandan, P. Anitha, G. Prakash, P. Vijayan, P. Viswanathamurthi, R.J.
Butcher, and J.G. Malecki, J. Mol. Catal. A 398 (2015) 312.
[32] W.-H. Sun, M. Shen, W. Zhang, W. Huang, S. Liu, C. Redshaw, Dalton Trans. 40
(2011) 2645.
[33] N. Ahmed, J.J. Levison, S.D. Robinson, M.F. Uttley, Inorg. Synth. 15 (1974) 45.
[34] R.A. Sanchez-Delgado, W.Y. Lee, S.R. Choi, Y. Cho, M.J. Jun, Trans. Met. Chem. 16
16

ACCEPTED MANUSCRIPT
(1991) 241.
[35] G. M. Sheldrick, Acta Crystallogr. A 64 (2008) 112.
[36] X. Li, B. Zhou, J. Zhang, M. She, S. An, H. Ge, C. Li, B. Yin, J. Li, Z. Shi, Eur. J. Org.
Chem. (2012) 1626.
[37] V.P. Singh, A. Singh, Russ. J. Coord. Chem. 34 (2008) 374.
[38] K. Nareshkumar, R. Ramesh, Polyhedron 24 (2005) 1885.
[39] M. Muthukumar, P. Viswanathamurthi, Spectrochim. Acta A 74 (2009) 454.
[40] M. Mishra, Monicasani, Metal-Based Drugs. 10 (2008) 1155.
[41] H.S. Abbo, S.J.J. Titinchi, R. Prasad, S. Chand, J. Mol. Catal. A 23 (2005) 225.
[42] G. Csjernyik, A.H. Ell, L. Fadini, B. Pugin, J. Backvall, J. Org. Chem. 67 (2003) 1657.
[43] R. Ramesh, M. Sivagamasundari, Synth. React. Inorg. Met. Org. Chem. 33 (2003) 899.
[44] B.P. Lever, Inorganic Electronic Spectroscopy, 2nd Edn. Elisevier, New York (1984).
[45] F. Basuli, S.M. Peng, S. Bhattacharya, Inorg. Chem. 40 (2001) 1126.
[46] (a) L.D. Brown, S.D. Robinson, A. Sahajpal, J.A. Ibers, Inorg. Chem. 16 (1977) 2728.
(b) M.I. Bruce, J. Howard, I.W. Nowell, G. Shaw, P. Woodward, J. Chem. Soc.
Chem. Commun. (1972) 1041.
(c) A.C. Skapski and P. G. H. Troughton, Chem. Commun. (London) (1968) 1230.
[47] X. Fernandez, R. Fellous, E. Dunach, Tetrahedron Lett. 41 (2000) 3381.
[48] I. Mohammadpoor-Baltork, A.R. Khosropour, S.F. Hojati, Catal. Commun. 8 (2007)
200.
[49] A. Shaabani, M. Seyyedhamzeh, A. Maleki, F. Rezazadeh, Appl. Catal. A 358
(2009) 146.
[50] S. Kumar, K. Kandasamy, H.B. Singh, R.J. Butcher, New J. Chem. 28 (2004) 640.
[51] T. Bodner, L. Ellmaier, V. Schenk, J. Albering, F. Wiesbrock, Polym. Int. 60 (2011)
1173.
[52] G.K. Jnaneshwara, V.H. Deshpande, M. Lalithambika, T. Ravindranathan, A.V.
Bedekar, Tetrahedron Lett. 39 (1998) 459.
[53] H. Witte, W. Seeliger, Angew. Chem. Int. Ed. 11 (1972) 287.
[54] J.A. Seijas, M.P. Vazquez-Tato, J. Crecente-Campo, Tetrahedron 64 (2008) 9280.
[55] X.N. Li, B.Y. Zhou, J. Zhang, M.Y. She, S.J. An, H.X. Ge, C. Li, B. Yin, J.L. Li, Z. Shi,
Eur. J. Org. Chem. (2012) 1626.
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Table 1
Crystal data and structure refinement parameters for the complex 2.
2
Empirical formula
Formula weight
Colour
C59H53ClN2O2P2Ru
1020.49
Red
Crystal dimensions (mm3)
Temperature (K)
Wavelength (Å)
Crystal system
0.44
× 0.14 × 0.12
295(2)
0.71073
Triclinic
P-1
Space group
Unit cell dimensions (Å, °)
a = 10.16019(16)
b = 15.0903(2)
c = 17.1169(3)
α = 90.5681(13)
β = 103.4832(14)
γ = 95.6632(13)
2538.10(7)
Volume Å3
Z
2
Calculated density (Mg/m3)
Absorption coefficient (mm-1)
F(000)
1.337
0.469
1056
Theta range for data collection (°)
Absorption correction
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
R indices [I>2σ(I)]
R indices (all data)
3.0811-34.6078
Multi-scan
Full-matrix least squares on F2
8804/0/608
1.109
R1 = 0.0493, wR2 = 0.1143
R1 = 0.0635, wR2 = 0.1200
18

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Table 2
Selected bond lengths (Å) and angles (°) for the complex 2.
Ru1-P1
2.4037(10)
P1-Ru1-P2
175.55(4)
Ru1-P2
Ru1-O2
Ru1-N1
2.4108(10)
2.083(2)
2.123(3)
P1-Ru1-C1
P2-Ru1-C1
P1-Ru1-Cl1
90.21(13)
93.24(13)
89.79(3)
Ru1-C1
Ru1-Cl1
O1-C1
1.830(4)
2.4089(9)
1.148(5)
P2-Ru1-Cl1
P1-Ru1-N1
P2-Ru1-N1
87.46(3)
91.29(8)
90.71(8)
O2-C9
N1-C2
1.305(4)
1.333(5)
P1-Ru1-O2
P2-Ru1-O2
87.59(7)
88.86(7)
N1-C10
1.386(5)
N1-Ru1-O2
79.74(10)
N1-Ru1-C1
N1-Ru1-Cl1
O2-Ru1-C1
102.62(15)
168.40(9)
176.81(14)
O2-Ru1-Cl1
O2-Ru1-N1
88.77(7)
79.74(10)
C1-Ru1-Cl1
88.92(13)
19

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Table 3
Optimization of reaction conditions.
O
N
Catalyst 1
H2N
OH
CN
+
Solvent free
Catalyst
loading (M%)
Substrate
ratio
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 2
1 : 1
1 : 3
1 : 4
1 : 5
1 : 3
1 : 3
Entry
Time (h) Temp (°C)
Yield (%)a
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22b
23c
2
3
4
5
6
7
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
70
70
70
70
70
70
50
60
80
90
100
110
90
90
90
90
90
90
90
90
90
90
90
2
2
2
2
2
2
2
2
2
2
2
2
1
3
4
5
-
14
20
31
39
39
39
04
11
44
57
57
58
32
64
72
72
08
46
87
87
88
-
4
4
4
4
4
4
38
aIsolated yield.
bIn presence of quinolinolate ligand, HL1.
cIn presence of precursor complex, [RuHCl(CO)(PPh3)3].
20

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Table 4
Selection of favorable catalysta.
Entry
Catalyst
Yield (%)b
1
2
3
4
87
83
77
72
1
2
3
4
aReaction conditions: Benzonitrile (1 mM), ethanolamine (3 mM) and catalyst (4 M%) refluxed
at 90 °C for 5 h.
bIsolated yield.
21

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Table 5
Synthesis of 2-oxazolines by ruthenium(II) catalysta.
O
Catalyst 1 (4 M%)
OH
H2N
+
CN
R
R
Solvent free
5 h, 90 °C
N
Entry
1
R
Yield (%)b
87
Phenyl
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
4-Nitrophenyl
4-Chlorophenyl
4-Acetylphenyl
4-Formylphenyl
4-Carboxylphenyl
4-Methylphenyl
4-Methoxyphenyl
4-Aminophenyl
4-Hydroxyphenyl
2-Naphthyl
4-Pyridyl
2-Thiophenyl
2-Aminophenyl
2-Methylphenyl
2-Chlorophenyl
97
90
92
95
94
83
81
87
86
91
89
87
63
60
68
aReaction conditions: Nitrile (1 mM), ethanolamine (3 mM), catalyst (4 M%) refluxed at 90 °C
for 5 h.
bIsolated yield.
22

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R
CH
N
R
N
CO
Cl
[RuHCl(CO)(EPh3)3]
Ru
+
O
Ph3E
Ethanol
Product 1
Reflux, 4 h
N
R
R
OH
N
R
N
CH
R
EPh
3 CO
N
O
Ru
Cl
EPh3
Product 2
[RuCl(CO)(EPh3)2(L1)] (1 & 3)
[RuCl(CO)(EPh3)2(L2)] (2 & 4)
E = P or As; R = Me (L1), iPr (L2)
Scheme 1. Synthetic route for ruthenium(II) complexes.
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O
N
EPh3
Cl
Ru
ArCN
EPh3
Ph3E
CO
OH
O
N
H2N
O
ArCN
Ar
N
NC Ar
Cl
Ru
Ph3E
CO
NH3
Ar
(I)
O
H
O
H2N
Ar
O
H
N
N
N
H
NH
Ru
CO
Ph3E
Cl
Ar
H2N
O
O
N
(II)
HN
Ru
Ph3E
Cl
CO
(III)
E = P or As
Scheme 2. Possible mechanism for ruthenium(II) catalyzed synthesis of 2-oxazoline.
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Figure 1. ORTEP view of complex 2. Thermal ellipsoids were drawn at 25% probability level.
The hydrogen atoms were omitted for clarity.
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Research Highlights
•
•
•
•
Synthesis of new ruthenium(II) carbonyl complexes.
Spectral characterization and crystal structure determination of the complexes.
Catalytic evaluation of Ru(II) complexes in the synthesis of 2-oxazolines.
Recovery and recycling of catalyst.