Half-sandwich ruthenium complexes with oxygen–nitrogen mixed ligands as efficient catalysts for nitrile hydration reaction

Article abstract of DOI:10.1016/j.poly.2017.09.007

Three ruthenium(II) p-cymene complexes containing oxygen–nitrogen mixed ligands [Ru(p-cymene)LCl] [HL = 2-(4,5-dihydrooxazol-2-yl)phenol (2a); HL = 2-(4,5-dihydrothiazol-2-yl)phenol (2b); HL = 2-(5,6-dihydro-4H-1,3-oxazin-2-yl)phenol (2c)] have been synthesized and characterized. All half-sandwich ruthenium complexes were fully characterized by ¹H and ¹³C NMR spectra, elemental analyses and infrared spectrometry. The molecular structure of ruthenium complex 2c was further confirmed by single-crystal X-ray diffraction methods. Furthermore, these half-sandwich ruthenium complexes are active catalysts for the hydration of nitriles to amides in the presence of sodium hydroxide in isopropanol.

Full text of DOI:10.1016/j.poly.2017.09.007

Polyhedron 138 (2017) 1–6
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Half-sandwich ruthenium complexes with oxygen–nitrogen mixed
ligands as efficient catalysts for nitrile hydration reaction
⇑
Wei-Guo Jia , Shuo Ling, Shen-Jie Fang, En-Hong Sheng
College of Chemistry and Materials Science, Center for Nano Science and Technology, The Key Laboratory of Functional Molecular Solids, Ministry of Education, Anhui Laboratory
of Molecular-Based Materials (State Key Laboratory Cultivation Base), Anhui Normal University, Wuhu 241000, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 July 2017
Accepted 5 September 2017
Available online 12 September 2017
Three ruthenium(II) p-cymene complexes containing oxygen–nitrogen mixed ligands [Ru(p-cymene)LCl]
[HL = 2-(4,5-dihydrooxazol-2-yl)phenol (2a); HL = 2-(4,5-dihydrothiazol-2-yl)phenol (2b); HL = 2-(5,6-
dihydro-4H-1,3-oxazin-2-yl)phenol (2c)] have been synthesized and characterized. All half-sandwich
ruthenium complexes were fully characterized by 1H and 13C NMR spectra, elemental analyses and infra-
red spectrometry. The molecular structure of ruthenium complex 2c was further confirmed by single-
crystal X-ray diffraction methods. Furthermore, these half-sandwich ruthenium complexes are active cat-
alysts for the hydration of nitriles to amides in the presence of sodium hydroxide in isopropanol.
Keywords:
Half-sandwich
Ruthenium
Complex
2
017 Elsevier Ltd. All rights reserved.
`
Catalyst
Nitrile
1
. Introduction
dihydrothiazol-2-yl)phenol (2b); HL = 2-(5,6-dihydro-4H-1,3-oxa-
zin-2-yl)phenol (2c)] and explored their catalytic activities for
the hydration of nitriles to aromatic amides. The half-sandwich
ruthenium complex catalysts allowed the hydration of nitriles to
proceed in the presence of sodium hydroxide with high yields in
isopropanol as solvent. This catalytic system was found to be effi-
cient toward the reduction of various nitriles substrates. Moreover,
the solid-state structure of complex 2c was confirmed by single-
crystal X-ray crystallography and the resolved structures reveal
that the complex adopt the three-legged piano-stool conformation
with a six-membered metallocycle formed by coordination of the
oxygen–nitrogen mixed ligands to the metal centers.
Half-sandwich ruthenium complexes are useful organometal-
lics compounds which are widely used as organic transformation
catalysts in construction CAC and C-heteroatom bond through
the direct CAH bond activation [1], CAN bonds formation from
alcohols and amines [2], transfer hydrogenation of ketones [3],
nitroarene reduction [4] and water oxidation [5]. Many efficient
ruthenium complexes have been synthesized and applied to vari-
ous organic transformations. Phenolate-oxazoline compounds are
oxygen–nitrogen mixed ligands that are readily modifiable
through changing the starting amino alcohol to allow fine tuning
of steric and electronic properties of the transition metal com-
plexes [6]. Exploring the catalytic activities of half-sandwich ruthe-
nium complexes with oxygen–nitrogen mixed ligands would be
interesting.
2
. Experimental
2.1. Materials and physical measurements
Amides are important building block in the preparation of poly-
mers, agrochemicals and pharmaceuticals [7]. The most widely
used method for the synthesis of amides is the hydration of nitriles
with transition metal catalysts, which is an ideal atom economical
reaction and sustainable method for the preparation of amides [8].
Ruthenium-based complexes are all good catalysts for the hydra-
tion of nitriles due to their high catalytic activity [9,10].
Herein, we have synthesized three half-sandwich ruthenium
complexes with oxygen–nitrogen mixed ligands [Ru(p-cymene)
LCl] [HL = 2-(4,5-dihydrooxazol-2-yl)phenol (2a); HL = 2-(4,5-
All the operations were carried out under a pure nitrogen atmo-
sphere using standard Schlenk techniques. All solvents were puri-
fied and degassed by standard procedures. The starting materials
[
1
2
Ru(p-cymene)(l-Cl)Cl] [11] and oxygen–nitrogen mixed ligands
a [12], 1b [13] and 1c [14] were synthesized according to proce-
1
13
dures described in the previous literature. H and C NMR were
recorded on a 300 MHz or 500 MHz NMR spectrometer at room
temperature. Chemical shifts (d) are given in ppm relative to inter-
1
13
nal TMS and are internally referenced to residual H and C sol-
vent resonances. IR spectra were recorded on a Niclolet AVATAR-
360IR spectrometer. Elemental analyses were performed on a Per-
kinElmer 2400 CHN analyzer.
⇑
Corresponding author. Fax: +86 0553 3869302.
E-mail address: wgjiasy@mail.ahnu.edu.cn (W.-G. Jia).
https://doi.org/10.1016/j.poly.2017.09.007
`
277-5387/ 2017 Elsevier Ltd. All rights reserved.
0

2
W.-G. Jia et al. / Polyhedron 138 (2017) 1–6
2.2. Synthesis of half-sandwich ruthenium complexes 2a–2c
2.3.4. 4-Iodobenzamide
1
H NMR (300 MHz, CDCl
3
): d 7.83(d, J = 6.0 Hz, 2H), 7.54 (d,
A solution of [Ru(p-cymene)(
oxygen–nitrogen mixed ligand (0.60 mmol), and K
.60 mmol) in CH CN (15 mL) was purged with N and then stirred
at 353 K for 3 h. The crude reaction mixture was loaded onto a col-
umn of silica gel and purified by column chromatography to give
l
-Cl)Cl]
2
(153.0 mg, 0.25 mmol),
J = 6.0 Hz, 2H), 5.86(br, 2H).
2
CO (96.5 mg,
3
0
3
2
2
.3.5. 3-Bromobenzamide
1
3
H NMR (300 MHz, CDCl ): d 7.96(s, 1H), 7.74(d, J = 9.0 Hz, 1H),
7
.67 (d, J = 9.0 Hz, 1H), 7.33(t, 1H), 6.01(br, 2H).
the reddish brown half-sandwich ruthenium complex.
1
2
a, Yield: (160.0 mg, 74%). H NMR (300 MHz, CDCl
3
) d 7.42 (d,
2
.3.6. Benzamide
J = 7.5 Hz, 1H), 7.15 (t, 1H), 6.96 (d, J = 6.3 Hz, 1H), 6.40 (t, 1H), 5.50
d, J = 4.5 Hz, 1H), 5.46 (d, J = 4.5 Hz, 2H), 5.37 (d, J = 4.5 Hz, 1H),
.56 (t, 2H), 4.44 (t, 2H), 2.86 (m, 1H), 2.21 (s, 3H),1.31 (d,
1H NMR (300 MHz, CDCl
3
): d 7.82(d, J = 6.0 Hz, 2H), 7.53(d,
(
J = 6.0 Hz, 1H), 7.44 (t, 2H), 6.12(br, 2H).
4
13
J = 5.0 Hz, 3H), 1.26 (d, J = 4.9 Hz, 3H); C NMR (125 MHz, CDCl
3
)
2
.3.7. 2-Methylbenzamide
d 168.91, 164.43, 134.39, 129.31, 123.55, 114.11, 109.67, 101.99,
1
3
H NMR (300 MHz, CDCl ): d 7.45(d, J = 7.5 Hz, 1H), 7.32 (t, 1H),
9
2
3
1
7.13, 83.26, 82.48, 81.70, 81.06, 67.43, 59.30, 31.18, 22.67,
7
.21(t, 2H), 5.97(br, 2H), 2.49(s, 3H).
2.55, 18.77; Anal. Calc. for C19
H22NO
2
RuCl: C, 52.71; H, 5.12; N,
À1
.24. Found: C, 52.70; H, 5.16; N, 3.27. IR (KBr, cm ) : 2968 (m)
629 (vs), 1544 (m), 1473 (s), 1441(s), 1391 (m), 1345 (s), 1244
2
.3.8. 3-Methylbenzamide
1
3
H NMR (300 MHz, CDCl ): d 7.64(s, 1H), 7.58 (s, 1H), 7.33(s,
(
s), 1154 (w), 1074 (s), 927 (m), 854 (m), 755 (s), 680 (w), 571 (w).
1
2
H), 6.10(br, 2H), 2.39(s, 3H).
2
b, Yield: (161.4 mg, 72%). H NMR (500 MHz, CDCl
3
) d 7.23 (d,
J = 6.0 Hz, 1H), 7.14 (d, J = 6.0 Hz, 1H), 7.00 (d, J = 9.0 Hz, 1H), 6.42
(
2
d, J = 6.0 Hz, 1H), 5.39 (m, 3H), 5.19 (d, J = 10.0 Hz, 1H), 4.73 (m,
2.3.9. 4-Methylbenzamide
H NMR (300 MHz, CDCl ): d 7.72(d, J = 9.0 Hz, 2H), 7.25 (d,
J = 9.0 Hz, 2H), 6.09(br, 2H), 2.39(s, 3H).
1
3
1
H), 3.41 (m, 2H), 2.75 (m, 1H), 2.14 (s, 3H), 1.21 (m, 6H);
) d 169.85, 166.77, 134.33, 132.06, 124.06,
18.56, 114.98, 102.50, 97.44, 83.17, 82.47, 81.80, 81.00, 70.48,
1.19, 30.53, 23.14, 22.18, 18.98. Anal. Calc. for C19 22ClNORuS:
C
3
NMR (125 MHz, CDCl
1
3
3
H
2
.3.10. 2-Aminobenzamide
C, 50.83; H, 4.94; N, 3.12. Found: C, 50.250; H, 5.10; N, 3.22. IR
1
3
H NMR (300 MHz, CDCl ): d 7.37(d, J = 7.5 Hz, 1H), 7.23(d,
À1
(
KBr cm ): 3003 (m), 1628 (vs), 1542 (m), 1470 (s), 1441 (s),
J = 7.5 Hz, 1H), 6.67 (m, 2H), 5.70(br, 2H).
1
(
360 (m), 1242 (s), 1155 (s), 1050 (w), 853 (m), 751 (s), 686
m),571 (w).
c, Yield: (145.1 mg, 65%). H NMR (300 MHz, CDCl
J = 6.0 Hz, 1H), 7.11 (t, 1H), 6.97 (d, J = 9.0 Hz, 1H), 6.43 (t, 1H), 5.47
d, J = 6.0 Hz, 1H), 5.26 (s, 2H), 5.13 (d, J = 6.0 Hz, 1H), 5.26 (m, 4H),
.44 (s, 2H), 4.38 (s, 1H), 4.70 (t, 1H), 2.74 (t, 1H), 2.06 (s,3H), 1.86
2
.3.11. 4-(Trifluoromethyl)benzamide
1
2
3
) d 7.43 (d,
1
H NMR (300 MHz, CDCl
3
): d 7.94(d, J = 9.0 Hz, 2H), 7.74(d,
J = 9.0 Hz, 2H), 6.10(br, 2H).
(
4
1
3
2.4. X-ray crystallography for 2c
(
1
8
s, 2H), 1.16 (m, 6H); C NMR (125 MHz, CDCl
3
) d 170.26, 158.90,
33.11, 128.81, 123.71, 119.67, 114.75, 102.93, 96.58, 82.09, 81.99,
1.83, 80.56, 66.30, 52.23, 31.10, 23.53, 23.25, 22.00, 18.87; Anal.
Diffraction data of 2c were collected on a Bruker AXS SMART
APEX diffractometer, equipped with a CCD area detector using
Calc. for C20
3
1
H
24ClNO
2
Ru C19
H
22NO
2
RuCl: C, 53.75; H, 5.41; N,
À1
Mo Ka radiation (k = 0.71073 Å). All the data were collected at
.13. Found: C, 53.66; H, 5.20; N, 3.19. IR (KBr cm ): 2956 (m),
2
98 K and the structures were solved by direct methods and sub-
622 (vs), 1542 (m), 1465 (s), 1441 (s), 1366 (m), 1334 (m), 1242
2
sequently refined on F by using full-matrix least-squares tech-
niques (SHELXL) [16], SADABS absorption corrections were applied to
the data [17], all non-hydrogen atoms were refined anisotropically,
and hydrogen atoms were located at calculated positions. All calcu-
lation was performed using the Bruker Smart program.
(
s), 1160 (s), 1102 (s), 1022 (w), 858 (m), 751 (s), 686 (m), 571 (w).
2
.3. General procedure for the nitrile hydration with half-sandwich
ruthenium catalysts
To a stirred solution of half-sandwich ruthenium complex
0.25 mol%) in 2.0 mL of isopropanol were added NaOH (0.3 mmol)
3
. Result and discussions
(
and benzonitrile (0.3 mmol) followed by stirring for 4 h at 353 K.
After completion of the reaction (monitored by TLC), the resulting
solution was evaporated to dryness at reduced pressure. The crude
products loaded directly onto a column of silica gel and purified by
column chromatography to yield the corresponding amides [15].
The oxygen–nitrogen mixed ligands (1a–1c) were synthesized
in moderate to good yields according to literature methods. The
reddish brown half-sandwich ruthenium complexes (2a–2c) were
obtained by reaction of [Ru(p-Cymene)(
lents of the oxygen–nitrogen mixed ligands in the presence of
CO in CH CN under reflux for 3 h (Scheme 1). Ruthenium com-
2
l-Cl)Cl] with two equiva-
K
2
3
3
2
.3.1. 4-Fluorobenzamide
H NMR (300 MHz, CDCl ): d 7.82(t, 2H), 7.12(t, 2H), 5.98(br,
3
H).
plexes were isolated as pure complexes by chromatography on sil-
ica gel using EtOAC/petroleum ether as an eluent in yields of 65–
74%. All complexes have been characterized by IR, NMR spec-
troscopy as well as elemental analyses. The proton signals at
1
2
7
.42, 7.15, 6.96, 6.40, 5.50, 5.46, 5.37, 4.56, 4.44, 2.86, 2.21, 1.31,
2
.3.2. 4-Chlorobenzamide
1
and 1.26 ppm in the H NMR spectrum can be easily assigned to
each of the corresponding hydrogen of 2a, respectively. The proton
signals at 6.40–7.42 ppm are corresponds to the phenyl ring proton
of the phenoxide-oxazoline. Two doublets appear at d = 5.50 and
5.37 ppm with a coupling constant of J = 4.50 Hz, respectively,
which indicates the presence of cymene ring [18]. Compared with
the ligand 1a infrared spectrum, the OAH stretching vibration of
1
H NMR (300 MHz, CDCl
3
): d 7.77(d, J = 9.0 Hz, 2H), 7.44 (d,
J = 9.0 Hz, 2H), 5.94(br, 2H).
2
.3.3. 4-Bromobenzamide
1
H NMR (300 MHz, CDCl
3
): d 7.70(d, J = 8.4 Hz, 2H), 7.60 (d,
J = 8.4 Hz, 2H), 5.93(br, 2H).

W.-G. Jia et al. / Polyhedron 138 (2017) 1–6
3
OH
Ru Cl
N
X
2
2
O
Cl
N
X
Ru
X = O, 1a
X = S, 1b
CH CN, reflux
3
Cl
Cl
X = O, 2a
X = S, 2b
+
Ru
K CO
2 3
Cl
OH
N
2
O
Ru Cl
1c
2
O
N
O
2c
Scheme 1. Synthesis of ruthenium complexes with oxygen–nitrogen mixed ligands (2a–2c).
À1
3
186 cm disappear in complex 2a due to the coordination effect
of the ligand with the ruthenium metal center.
3.1. Structural description of 2c
X-ray diffraction of single crystals for complex 2c was obtained.
The crystals were grown by slow diffusion of diethyl ether into a
concentrated solution of the complexes in methanol solution. The
crystallographic data for half-sandwich ruthenium complex 2c
are summarized in Table 1. The molecular structure of 2c is shown
in Fig. 1.
As shown in Fig. 1, the Ru is surrounded by one chlorine atom,
one nitrogen atom and one oxygen atom from the phenoxide-oxa-
zoline ligand and one of the p-cymene rings. Both the ruthenium
centers have six-coordinate geometry assuming that the p-cymene
ring serve as three-coordinated ligand, which is common for
Table 1
a
Crystallographic data and structure refinement parameters for complex 2c.
2
c
Fig. 1. Molecular structure of complex 2c with thermal ellipsoids drawn at the 30%
level. All hydrogen atoms are omitted for clarity. Selected lengths (Å) and angles (°):
Ru1–O1 2.057(3), Ru1–N1 2.096(4), Ru1–Cl1 2.4174(16), N1–Ru1–O1 85.68(15),
N1–Ru1–Cl1 84.81(12), O1–Ru1–Cl1 84.16(12).
Empirical formula
Formula weight
Crystalsyst., Space group
a (Å)
b (Å)
c (Å)
C
20 2
H24ClNO Ru
446.92
triclinic, P1ꢀ
11.6633(14)
11.7341(14)
15.4230(18)
73.71(1)
84.60(2)
76.68(2)
1970.46(40), 2
1.506
0.943
half-sandwich ‘‘piano stool” structures. The RuAO distances
a
(°)
b (°)
(°)
(
2.057(3) Å) and RuAN distances (2.096(4) Å) are comparable to
those of half-sandwich ruthenium complex containing [N,O]
anionic bidentate ligands [19].
c
3
V (Å ), Z
D
l
calc (mg/m3)
(Mo K ) (mm
À1
a
)
F(000)
h range (°)
912
1.38–25.00
3.2. Catalytic hydration of nitriles
Limiting indices
Reflections/unique [Rint
Completeness to h (°)
Data/restraints/parameters
À13, 13; À13, 13; À18, 18
6914/4989 [0.0447]
25.00
6914/0/415
1.042
With the three half-sandwich ruthenium complexes in hand,
their abilities to catalyze the hydration of nitriles were examined.
The hydration of 4-bromobenzonitrile was selected as the model
reaction for establishing the best reaction conditions. As shown
in Table 2, the half-sandwich ruthenium complex 2c was found
to be very active toward the nitrile hydration. We examined the
effect of catalyst loading with the aid of ruthenium catalyst 2c.
]
2
Goodness-of-fit (GOF) on F
R
R
1
, wR
, wR
2
[I > 2(I)]a
(all data)
R
R
1
= 0.0454, wR
= 0.0720, wR
2
= 0.1084
= 0.1218
1
2
1
2
a
2
2
2
2 2
R
1
=
R
||F
o
| À |F
c
||/R
|F
o
|; wR
2
= [R
w(|F
o
| À |F

4
W.-G. Jia et al. / Polyhedron 138 (2017) 1–6
Table 2
Table 3
Screening of 4-bromobenzonitrile hydration reaction conditions using half-sandwich
Screening of substrates for nitrile hydration reaction catalyzed by ruthenium complex
2c.
ruthenium complex catalyst.a
a
CN
Br
CONH2
Br
Entry
1
Substrate
Product
Yield (%)b
76
Ru catalysts
F
CN
CN
CN
CN
F
CONH2
2
3
4
5
84
93
90
85
solvents, base, temperatrue
Cl
Br
Cl
Br
CONH2
CONH2
Entry
Catalyst
Loading (mol %)
Solvent
Yield (%)b
1
2
3
4
5
6
7
8
9
[Ru(p-Cymene)(
l
-Cl)Cl]
2
2
IPA
IPA
IPA
IPA
IPA
IPA
IPA
IPA
IPA
43
74
96
68
94
94
92
85
80
32
33
44
70
10
I
I
CONH2
2a
2c
2b
2c
2c
2c
2c
2c
2c
2c
2c
2c
2c
2c
2c
2c
2c
2c
2c
2
2
2
1
0.5
0.25
0.1
0.05
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
Br
Br
CN
CN
CONH2
CONH2
6
7
92
72
c
10
11
12
13
14
15
16
17
18
19
20
2
H O
DMF
CH OH
3
CN
CN
CONH2
CONH2
EtOH
Toluene
IPA
8
9
87
c
8
d
e
f
IPA
IPA
IPA
IPA
76
12
92
91
81
g
CN
CONH2
NR
NR
h
IPA
1
0
1
a
CN
CONH2
Reaction conditions: 0.3 mmol 4-bromobenzonitrile, 0.3 mmol NaOH, Ru catalysts,
solvents (2 mL), 353 K. Isolated yield; 12 h; c298 K; d323 K; 393 K; 0.3 mmol
b
c
e
f
t
g
h
NaO Bu; 0.3 mmol Na
2
CO
3
;
0.3 mmol NEt
3
.
NH2
NH2
1
77
F3C
CN
F3C
CONH2
The reactions were carried out with different amount of catalyst
ranging from 2 to 0.05 mol%. The high yields were obtained with
the catalyst ranging from 2 to 0.25 mol%. When the catalyst load-
ing was further lowered to 0.05 mol% the complex showed the sim-
ilar activity with longer reaction time (Table 2, entry 9). It is well-
known that the solvent can have a profound effect on the rate of
the hydration reaction. Hence, we interested in exploring the sol-
vent-dependent differences in activity of catalyst 2c on carrying
out at the model hydration of nitrile in the most frequently used
aReaction conditions: 0.3 mmol benzonitrile derivative, 0.3 mmol NaOH, 2c
0.25 mol %), IPA (2 mL), 353 K. bIsolated yield.
(
desired products in high yields. The reaction is tolerant of a range
of aromatic functional groups including aryl halides (Table 3,
entries 1–5) and methyl (Table 3, entries 7–9) and 2-aminoben-
zonitrile. It appeared that the steric hindrance of benzonitrile had
an influence on the catalytic activities of the transformation from
benzonitrile to benzamide. The p- and m-benzonitrile did not ham-
per the reaction (Table 3, entries 7–9). However, the moderate
yields were observed for benzonitrile with electron-withdrawing
groups trifluoromethyl (Table3, entry 11).
2
solvents such as H O, DMF, EtOH, MeOH, iPrOH (IPA), and toluene.
The results are given in Table 2. Toluene, DMSO, and MeOH invari-
ably gave poor yields (Table 2, entries 10–14). iPrOH was found as
the best solvent for the hydration of nitrile within 4 h (Table 2,
entry 7). While, ethanol resulted in moderate yields (Table 2, entry
The complete elucidation of the mechanism has not been
undertaken for this hydration of nitriles reaction. On the basis of
the present experimental results and those previously observed
1
3). The yields improved slightly when reaction temperature was
raised (Table 2, entries 15–17). However, the yield was decrease
when the reaction temperature further raised to 393 K (Table 2,
entry 17). The choice of base is critical to the reaction since no
[
10,20], we suggest the half-sandwich ruthenium hydride gener-
ated from 2c as the active catalyst species in the present catalytic
cycle. This hypothesis is supported by in situ NMR studies on the
mechanism of proton transfer from isopropanol to Ru metal center.
The proton signal at À10.17 ppm corresponds to hydride, which
indicates the presence of RuAH intermediate [21]. Based on this
assumption, the mechanism shown in Scheme 2 is proposed.
reaction was observed when changing NaOH for the weaker base
t
Na
2
CO
3
or Et
3
N (Table 2, entries 18–20). The strong base NaO Bu
and NaOH facilitate the formation of a ruthenium alkoxide by
abstracting the proton of the isopropanol. The alkoxide then under-
goes a b-elimination to give a RuAH active species (Scheme 2).
With the optimal reaction conditions in hand, we started to
expand the scope and efficiency of this methodology, we employed
several nitriles to evaluate the scope of the catalyst 2c using
4. Conclusions
0
.25 mol% of catalyst with the reaction of 4 h at 353 K with iso-
propanol as a solvent. As shown in Table 3, the catalyst 2c was
found to be very active toward the reduction of various nitrile com-
pounds. A series of functionalized amides were obtained in good to
excellent yields. Electron-withdrawing and electron-donating
substituent on the aromatic backbone were able to provide the
In summary, we have synthesized and characterized three novel
half-sandwich ruthenium complexes with oxygen–nitrogen mixed
ligands and evaluated their catalytic activities in hydration of
nitriles reaction using isopropanol as solvent. The hydration of
nitriles reaction offers varied functional group compatibility and

W.-G. Jia et al. / Polyhedron 138 (2017) 1–6
5
Scheme 2. A possible catalytic cycle for the hydration of benzonitrile by complex 2c.
provides amides in good to excellent yields. We tentatively pro-
pose a half-sandwich ruthenium hydride complex as the active
species in catalyzing the hydration of nitriles and further mecha-
nistic studies is in progress.
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
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