Catalytic amination of benzyl alcohol using ruthenium cymene compounds containing bidentate N,O-donor ancillary ligands

Article abstract of DOI:10.1016/j.jorganchem.2018.02.029

A series of ruthenium-cymene derivatives subjecting [Ru(η⁶-cymene)Cl₂]₂ and substituted bidentate N,O donor precursors have been synthesized and characterized. Reacting [Ru(η⁶-cymene)Cl₂]₂ with two equivalents the lithium salt of phenyl keto-amine ligands LiL₁～LiL₃ resulted in the formation of [Ru(η⁶-cymene)(L)Cl] (1–3). Similarly, the reaction between [Ru(η⁶-cymene)Cl₂]₂ and two equivalents of LiL₄ or NaL₅ afforded compounds {Ru(η⁶-cymene)[L₄)]Cl} (4) and [Ru(η⁶-cymene)(L₅)Cl] (5). The ¹H NMR chemical shifts of aromatic protons of the cymene fragment for compounds 1–5 fell in the range δ 5.54–3.58, showing chemical shifts farther upfield than the corresponding protons of [Ru(η⁶-cymene)Cl₂]₂ due to the intramolecular ring current effect. The 2,6-diisopropylphenyl substituted pheny lketo-amine ligand of compound 3 shows a slow C-N bond rotation with the rotation rate constant at ca. 4.62 s^?1. The catalytic aminations of benzyl alcohol with benzylamine using compounds 1–3 as catalysts resulted in higher conversion than using compounds 4 and 5. Two products, PhCH = NCH₂Ph and HN(CH₂Ph)₂ were detected, with PhCH = NCH₂Ph being the major product. When benzyl alcohol was reacted with phenylamine in the presence of compounds 1–5, the conversions are all greater than 60% and PhCH = NPh was the major product. While sterically hindered 2,6-diisopropylaniline appeared in alcohol amination reactions in the presence of catalysts, no imine or amine products were detected.

Full text of DOI:10.1016/j.jorganchem.2018.02.029

Journal of Organometallic Chemistry 861 (2018) 10e16
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Catalytic amination of benzyl alcohol using ruthenium cymene
compounds containing bidentate N,O-donor ancillary ligands
a
a
b
a
a
Chi-Meng Hsiao , Yun-Fan Chen , Chia-Her Lin , Ching-Han Hu , You-Ru Cai ,
Jui-Hsien Huang
a
a, *
Department of Chemistry, National Changhua University of Education, Changhua, 50058 Taiwan
Department of Chemistry, Chung-Yuan Christian University, Chun-Li 320, Taiwan
b
a r t i c l e i n f o
a b s t r a c t
A series of ruthenium-cymene derivatives subjecting [Ru( 6
donor precursors have been synthesized and characterized. Reacting [Ru(
equivalents the lithium salt of phenyl keto-amine ligands LiL ~LiL resulted in the formation of [Ru(
-cymene)Cl and two equivalents of LiL
Article history:
Received 7 August 2017
Received in revised form
2 2
h -cymene)Cl ] and substituted bidentate N,O
6
h
2 2
-cymene)Cl ] with two
6
1
3
h -
20 February 2018
6
cymene)(L)Cl] (1e3). Similarly, the reaction between [Ru(
h
2
]
2
4
or
)Cl] (5). The H NMR
chemical shifts of aromatic protons of the cymene fragment for compounds 1e5 fell in the range 5.54
-cymene)Cl
due to the intramolecular ring current effect. The 2,6-diisopropylphenyl substituted pheny lketo-amine
Accepted 21 February 2018
6
6
1
5 4 5
NaL afforded compounds {Ru(h -cymene)[L )]Cl} (4) and [Ru(h -cymene)(L
d
6
e3.58, showing chemical shifts farther upfield than the corresponding protons of [Ru(
h
2 2
]
Keywords:
Intramolecular ring current effect
Spin saturation transfer
Alcohol amination
Ruthenium
ꢀ
1
ligand of compound 3 shows a slow C-N bond rotation with the rotation rate constant at ca. 4.62 s . The
catalytic aminations of benzyl alcohol with benzylamine using compounds 1e3 as catalysts resulted in
higher conversion than using compounds 4 and 5. Two products, PhCH ¼ NCH
2 2 2
Ph and HN(CH Ph) were
Ph being the major product. When benzyl alcohol was reacted with phe-
detected, with PhCH ¼ NCH
2
nylamine in the presence of compounds 1e5, the conversions are all greater than 60% and PhCH ¼ NPh
was the major product. While sterically hindered 2,6-diisopropylaniline appeared in alcohol amination
reactions in the presence of catalysts, no imine or amine products were detected.
©
2018 Elsevier B.V. All rights reserved.
1
. Introduction
direct conversion of alcohol to amines, ruthenium-arene complexes
have been applied with the combination of phosphine ligands [11].
We have been using bidentate keto-amine ligands (N,O-bidentate
ligands) to bind with metals forming new organometallic com-
plexes and we have studied their reactivity towards small mole-
cules [12]. The merits of using N,O-bidentate ligands are that the
ligands are readily synthesized and their electronic and electronic
properties can be adjusted. In this present contribution, we have
embarked on the synthesis of Ru-arene complexes incorporating
The conversion of alkyl or aryl alcohol to an amine by a con-
ventional method of organic synthesis generally requires many
efforts. A severe condition such as high pressure and high tem-
perature are required and also produces a large amount of chemical
waste [1]. Methods used for the synthesis of alkyl or aryl amines
were developed as Gabriel reactions [2] and Mitsunobu reactions
[
3]. However, the direct conversion of alcohol to amine is very
necessary due to economic and environmental reasons, and this
can be achieved with the addition of catalysts. Metal catalysts for
the direct conversion of alcohol to amine should include Fe [4], Rh
2 2
the starting material [Ru(cymene)Cl ] and N,O-bidentate ligands
(as shown in Scheme 1). Herein, we also described the phenome-
non of intramolecular ring current effect of cymene aromatic pro-
tons observed with the N-substituted phenyl ring. In addition, we
use the spin saturation transfer method for determining the C-N
bond rotation of related ruthenium compounds. Furthermore, we
have investigated the catalytic amination of benzyl alcohol with
different primary-amines, employing the ruthenium derivatives as
catalysts.
[
5], Ir [6] and Ru [7], etc. The ruthenium complexes have been
applied in many catalytic reactions, such as aldehyde-water shift
reaction [8], the transformation of alcohols [9], dehydrogenation of
formic acid [10], etc. As for the ruthenium complexes used for the
*
Corresponding author.
E-mail address: juihuang@cc.ncue.edu.tw (J.-H. Huang).
https://doi.org/10.1016/j.jorganchem.2018.02.029
022-328X/© 2018 Elsevier B.V. All rights reserved.
0

C.-M. Hsiao et al. / Journal of Organometallic Chemistry 861 (2018) 10e16
11
Scheme 1. Imine ligand systems used for synthesizing ruthenium compounds.
2
. Results and discussion
appeared at
d
9.05 and 9.52, respectively. The 1H NMR spectra of
5.40
compounds 1e3 all showed a characteristic singlet at ca.
d
2
.1. Synthesis of compounds 1e5
representing the methine signal of the ketoaminate backbone of
the N,O bidentate ligand. We observed that the aromatic protons of
the cymene fragment for compounds 1e5 fell in the range
A series of ruthenium-cymene compounds 1e5 incorporating
bidentate N,O donor precursors were synthesized and character-
d 5.54e3.58, showing chemical shifts farther upfield than the cor-
6
6
ized as shown in Scheme 2. Reacting [Ru(
two equivalents of LiL ~LiL , obtained from the reaction of
H ~ L H and n-BuLi, resulted in the formation of [Ru(
h
-cymene)Cl
2
]
2
[13] with
2 2
responding protons of [Ru(h -cymene)Cl ] which were located at
1
3
d
5.31 and 5.45 due to the intramolecular ring current effect. The
6
L
1
3
h
-cyme-
detailed description of the ring current effects will be discussed
later.
ne)(L)Cl] (1, 37.7% yield; 2, 31.9% yield; 3, 52.4% yield). A similar
ruthenium compound has been reported by McGowan et al. [14].
Compounds 1e3 are readily soluble in methanol, methylene chlo-
2.3. Structural determinations of compounds 1e5
ride, and toluene, but insoluble in diethyl ether and heptane.
6
Similarly, the reaction between [Ru(
equivalents of LiL
h
-cymene)Cl
2
]
2
and two
Single-crystal X-ray diffraction analysis revealed that com-
6
4
afforded compound {Ru(
h
-cymene)[L )]Cl} (4)
4
pounds 1, 2, and 5 crystallized in the triclinic space group P-1
whereas compounds 3 and 4 crystallized in the monoclinic space
group P21/c and the hexagonal space group R-3, respectively. The
summary of X-ray crystal data and selected bond lengths and an-
gles are shown in Tables s1 and s2, respectively (supporting
information). The molecular geometries of 1e5 were quite
similar, as depicted in Figs. 1e5. The geometries of 1e5 resembled
three-legged piano stools on which the phenyl ring of the cymene
moiety acted as the raised surface. The distances between Ru atom
and the cymene ring center for compounds 1e5 were in the range
of 1.66e1.67 Å; no additional steric or electronic effects were
perceived in the bidentate N,O-ligand moiety. Similarly, the Ru-O
and Ru-Cl bond lengths of 1e5 were in the ranges of
2.049e2.056 Å and 2.397e2.441 Å, respectively, showing no steric
hindrance which could interrupt normal bonding ability between
Ru and O atoms. The RuꢀNketo-amine bond lengths of 1e3 varied
from 2.079 to 2.123 Å; however, due to bulky 2,6-diisopropylphenyl
which was recrystallized from a saturated toluene solution
ꢁ
at ꢀ20 C to give shiny red crystals (42.0% yield). The reaction of
6
6
[
Ru(
2 2 5
h -cymene)Cl ] and NaL generated compound [Ru(h -cym-
ene)(L
5
)Cl] (5) in 41.0% yield which was readily recrystallized from
ꢁ
methylene chloride at ꢀ20 C. Thermal stability test for all the
compounds shows no apparent decomposition was observed by
ꢁ
dissolving these compounds in CDCl
3
at 70 C for overnight.
2.2. NMR spectra data of compounds 1e5
1
13
The H and C NMR spectra of compounds 1e5 were recorded
1
in CDCl
of 1e5 all showed a septet and a doublet at ca.
.07e1.18, respectively, which corresponded to the methine and
3
to determine their possible structures. The H NMR spectra
d
2.66e2.89 and
1
methyl protons of the isopropyl fragments. The characteristic
chemical shifts for the CH¼N proton of compounds 4 and 5,
Scheme 2. Synthesis of compounds 1e5, all the yield of these compounds are included in parenthesis.

12
C.-M. Hsiao et al. / Journal of Organometallic Chemistry 861 (2018) 10e16
Fig. 1. The molecular geometry of 1. Thermal ellipsoids were drawn at 50% probability
level. Hydrogen atoms were omitted for clarity.
Fig. 5. The molecular geometry of 5. Thermal ellipsoids were drawn at 50% probability.
Hydrogen atoms were omitted for clarity.
groups in 3, the corresponding RuꢀN bond lengths were longer
than those in 1 and 2 [15].
2.4. Intramolecular ring current effect and theoretical calculations
We noticed that the cymene moiety of [Ru(h6-cymene)Cl
2
]
2
1
showed two H NMR resonances at
d 5.31 and 5.45 for the phenyl
protons. The upfield shifts occurred due to the nature of the
ruthenium atom which reduced the aromatic ring current effect
[16]. Interestingly, the chemical shift of the phenyl protons of the
cymene moiety for compounds 1e3 was more upfield shifted in
Fig. 2. The molecular geometry of 2. Thermal ellipsoids were drawn at 30% probability.
Hydrogen atoms were omitted for clarity.
6
2 2
comparison to that of compound [Ru(h -cymene)Cl ] and the
others [14a,17]. The intramolecular ring current effect was attrib-
uted to this upfield shift of the phenyl protons of the cymene
moiety. In compound 1, we observed that the corresponding
upfield-shifted proton was located just above the imine phenyl ring
(Fig. 6) and the strong ring current of the imine phenyl ring influ-
enced the phenyl protons of the cymene moiety, as shown in Fig. 7.
In order to elucidate the relationships among the stereo geome-
tries, the ring current effect, and the phenyl proton chemical shifts
of the cymene moieties for compounds 1e5, we performed theo-
retical calculations using the B3LYP/gen method along with 6-31G*
and LANL2DZ, for the rest of the atoms and the Ru atom, respec-
tively. The optimized geometries of 1e5 were very compatible with
X-ray crystal structures when compared with the selected bond
angles and bond lengths shown in Table 1. By using the optimized
geometries of 1e5, the relative positions of the imine phenyl ring
and the phenyl protons of the cymene moiety were calculated using
B3LYP/gen, SCRF¼(CPCM, solvent ¼ chloroform). In compounds 1,
Fig. 3. The molecular geometry of 3. Thermal ellipsoids were drawn at 50% probability.
Hydrogen atoms were omitted for clarity.
4, and 5, the cymene H4 protons were located above the imine
phenyl rings whereas, in compounds 2 and 3, the cymene H3
Fig. 4. The molecular geometry of 4. Thermal ellipsoids were drawn at 50% probability.
Hydrogen atoms were omitted for clarity.
Fig. 6. A perspective view of compound 1 showing one of the cymene phenyl ring
protons located just inside the ring current of the substituted phenyl ring.

C.-M. Hsiao et al. / Journal of Organometallic Chemistry 861 (2018) 10e16
13
following equation,
k ¼ (T1b ꢀ
)
1
x [I
ꢀ1]
0
/I
d
Where I
0 d
/I
¼ 5.65 and T1b ¼ 1.006 s; therefore, the rate constant for
ꢀ
1
the C-N bond rotation may be calculated as 4.62 s
.
2.6. Catalytic alcohol amination reactions
Amines are important intermediates in laboratories and in
chemical related industries for that these amines can be used for
synthesizing various biologically active compounds [22]. Convert-
ing alcohols to amines is a promising method to generate new
amines and heterogeneous catalysts are usually used for the re-
actions in the industry [23]. When using heterogeneous catalysts,
high temperature and high pressure are usually required for the
reaction conditions. Therefore, in searching of homogeneous cata-
lyst for the alcohol amination reactions, ruthenium complexes are
found to be good candidates which can effective converting of al-
cohols to amines under mild condition through a borrowing
hydrogen mechanism [24]. Therefore, we also investigated the
catalytic amination of benzyl alcohol [25] with a primary amine
using ruthenium compounds 1e5 as shown in Scheme 3 and the
results are shown in Table 3. The steric hindrance of the amines
played an important role on the amination of the alcohols under
catalytic conditions. Reactions are optimized using compound 1, as
shown in entries 1e5 in Table 3; KOH was chosen as the base and
reaction time was set at 24 h. While benzylamine was used to react
with benzyl alcohol, ruthenium compounds containing ketoamine
ligands (compounds 1e3) showed higher conversion than other
ruthenium compounds 4 and 5, with the conversion being as
Fig. 7. Intramolecular ring current effect of phenyl proton of cymene moiety by the N-
substituted phenyl ring.
protons were positioned above the imine phenyl rings. The phenyl
ring on the keto-amine backbone was perpendicular to the cymene
ring and made no contribution to the ring current effect towards
the phenyl protons of the cymene moiety. The calculated and
experimental phenyl proton chemical shifts of the cymene moiety
for compounds 1e5 are shown in Table 2. The calculated NMR
chemical shift data lightly differ from the experimental data,
however, the trend is inconsistent. From the relevant data, the
upfield shift of the phenyl proton of the cymene is clearly related to
the geometry and ring current strength of the imine phenyl ring.
2.5. Spin saturation transfer
The internal rotation on the C-N bond provides information that
extends our understanding of the conformational characteristics.
The related compounds show a dynamic equilibrium on the NMR
time scale [18]. However, there are barriers to rotation about the C-
N bond, which makes the rotation relatively slower due to the
formation of a partial C-N double bond from the electron reso-
nances [19] or by steric hindrance in molecular geometry [20]. ].
When measuring the 1H NMR chemical shifts in 3, three methine
higher as 99% within 24 h. Two products, PhCH ¼ NCH
2
Ph and
HN(CH Ph) Ph being the major
2
2
were detected, with PhCH ¼ NCH
2
product. However, when benzyl alcohol was reacted with phenyl-
amine and catalyzed by compounds 1e5, the conversions are all
greater than 60% and PhCH ¼ NPh was the major product (entry
13e17). It is interesting to note that with the sterically hindered
proton signals at
d 3.89, 3.24, 2.89 were observed and can be
2,6-diisopropylaniline appeared in the alcohol amination reactions
attributed to the great steric hindrance of the 2,6-
diisopropylphenyl groups with the cymene fragment. Methine
proton signals were not merged, even after increasing the tem-
in the presence of catalysts, no imine or amine products were
detected.
ꢁ
perature of the NMR probe at 55 C. The homonuclear decoupling
spectra of compound 3 were performed in order to differentiate the
three isopropyl groups. It is interesting to note that the transfer of
spin saturation occurred when the Ha decoupled and the Hb in-
tensity decreased, and vice versa. This phenomenon, ie transfer of
spin saturation [21], indicated that the rotation of the C-N bond
rotation slowed down on the NMR time scale but was still fast
enough for the decoupled protons to carry the memory of equalized
populations to non-decoupled protons. The spin-lattice relaxation
3. Conclusions
In conclusion, we highlight a convenient route for the prepa-
ration and characterization of ruthenium-cymene derivatives using
precursors of N,O donors. The versatility of the cymene-ruthenium
derivatives may play a promising role in the catalytic activity of the
amination reaction of alcohol, with the whole process serving as an
effective and economical route for this type of catalytic studies.
Interestingly, we used theoretical calculations to explain the effect
of the intramolecular ring current on the N-substituted phenyl ring,
which resulted in the phenyl protons of the cymene ring being
upfield shifted. The slow rotation of the C-N bond of the N,O-
time (T1b) of H
method. If the ratio of the initial intensity of H
final intensity of H resonance upon irradiating the H
/I , then the C-N bond rotation rate can be calculated using the
b
was equal to 1.006 s using the inversion recovery
resonance and the
resonance is
b
b
a
I
0 d
Table 1
ꢁ
Experimental and calculated (in parenthesis) bond lengths (Å) and angles ( ) for compounds 1e5.
ꢁ
bond length (Å)
bond angle ( )
Ru-Cl
Ru-O
Ru-N
N-Ru-O
Cl-Ru-O
Cl-Ru-N
1
2
3
4
5
2.43 (2.45)
2.44 (2.46)
2.45 (2.46)
2.40 (2.44)
2.42 (2.44)
2.04 (2.07)
2.05 (2.07)
2.05 (2.07)
2.05 (2.05)
2.05 (2.05)
2.08 (2.11)
2.08 (2.11)
2.12 (2.16)
2.14 (2.16)
2.12 (2.16)
89.08 (88.86)
88.71 (89.04)
87.02 (88.20)
79.18 (79.24)
79.24 (79.18)
85.28 (86.73)
86.18 (86.55)
83.37 (84.63)
84.46 (87.48)
85.22 (87.23)
84.35 (85.12)
83.10 (85.52)
87.18 (86.56)
87.52 (86.28)
85.72 (85.98)

14
C.-M. Hsiao et al. / Journal of Organometallic Chemistry 861 (2018) 10e16
Table 2
spectra were recorded using a Bruker Avance 300 spectrometer and
the chemical shifts were recorded in ppm relative to the residual
Calculated and experimental 1H NMR chemical shift of the aromatic protons of
cymene for compounds 1e5.
protons of CDCl
performed using a Heraeus CHN-OS Rapid Elemental Analyzer at
3
(
d
¼ 7.24, 77.0 ppm). Elemental analyses were
compound
Calculated H1, H2, H3, H4
4.69, 5.20, 5.08, 2.98
experimental
5.32 (d, 1H)
6
the Instrument Center of the NCHU. [(
h
-cymene)RuCl
2 2
] (cym-
5
5
3
.14 (d, 1H)
.03 (d, 1H)
.64 (d, 1H)
ene ¼ 4-isopropyltoluene) [13] and L
H ~ L H [26] were prepared
1
5
accordingly.
4
4
.2. Synthesis
.2.1. Synthesis of [Ru(
A Schenk flask charged with L
h
6-cymene)(L
1
)Cl] (1)
1
H (0.30 g, 1.3 mmol) and 15 mL of
5.80, 5.75, 3.70, 5.70
5.34 (d, 1H)
ꢁ
5
3
.16 (t, 2H)
.58 (d, 1H)
THF was cooled to 0 C and added n-BuLi (0.51 mL, 1.3 mmol). The
resulting solution was added dropwise to a THF (15 mL) solution of
6
ꢁ
[Ru(h -cymene)Cl ] (0.39 g, 0.63 mmol) at 0 C. After stirring 3 h,
2 2
all the volatiles were removed under vaccum and the resulting
residue was extracted with methylene chloride (3 ꢂ 10 mL) and
filtered through Celite. The filtrate was vaccum dried and residue
was recrstallized from a saturated toluene solution to yield 0.24 g of
5.73, 4.42, 3.29, 4.85
5.35 (s, 2H)
1
red crystals (37.7%). H NMR (CDCl
3
): 7.82e7.72 (m, 3H, Ph),
4
4
.92 (d, 1H)
.18 (d, 1H)
3
7
C
3
.39e7.21 (m, 7H, Ph), 5.40 (s, 1H, CCHC), 5.32 (d, JHH ¼ 8 Hz, 1H,
3
3
6
H
4
), 5.14 (d, JHH ¼ 8 Hz, 1H, C
6
H
4
), 5.03 (d, JHH ¼ 8 Hz, 1H, C
6
H
4
),
),
C
3
3
.64 (d, JHH ¼ 8 Hz, 1H, C
6
H
4
), 2.66 (sept, JHH ¼ 7 Hz, 1H, CHMe
2
1
3
1
.99 (s, 3H, cymene Me), 1.76 (s, 3H, Me), 1.17 (m, 6H, CHMe
2
).
NMR (CDCl
3
): 171.8 (C¼O), 164.7 (C¼N), 157.4 (Ph), 139.7 (Ph), 129.7
(
(
(
Ph), 129.4 (Ph), 127.9 (Ph), 127.8 (Ph), 127.0 (Ph), 126.2 (Ph), 125.5
Ph), 123.5 (Ph), 100.8 (Cipso), 96.3 (Cipso), 94.6 (CH), 87.3 (CH), 84.7
CH), 84.5 (CH), 79.4 (CH), 30.6 (CH), 24.8 (Me), 23.5 (Me), 21.0 (Me),
4.75, 5.59, 4.77, 3.84
5.33 (d, 1H)
5
4
4
.07 (d, 1H)
.65 (d, 1H)
.47 (d, 1H)
1
8.5 (Me). Anal. Calcd. for C26
H28ClNORu (507.04): C, 61.59; H, 5.57;
N, 2.76. Found: C, 60.96; H, 5.49; N, 2.97%.
4
.2.2. Synthesis of {Ru(
h
6-cymene)(L
Similar procedure as for synthesizing compound 1 was adopted.
2
)]Cl} (2)
6
L
2
H (0.30 g, 1.1 mmol), n-BuLi (0.45 mL, 1.1 mmol), and [Ru(
cymene)Cl (0.34 g, 0.56 mmol) were used. Compound 2 was
isolated in 31.9% yield (0.28 g). H NMR (CDCl
Ph), 7.30e7.18 (m, 4H, Ph), 6.99 (m, 2H, Ph), 5.41 (s, 1H, CCHC), 5.34
h -
4.51, 5.57, 4.60, 2.94
5.33 (d, 1H)
2 2
]
5
4
3
.00 (d, 1H)
.49 (d, 1H)
.78 (d, 1H)
1
3
): 7.83e7.74 (m, 3H,
3
(
(
(
(
1
1
8
1
5
d, JHH ¼ 8 Hz, 1H, C
6
H
4
), 5.16 (m, 2H, C
6
H
4
), 3.93 (s, 3H, OMe), 3.58
3
3
d, JHH ¼ 8 Hz, 1H, C
6
H
4
), 2.66 (sept, JHH ¼ 7 Hz, 1H, CHMe ), 1.97
2
13
s, 3H, Me), 1.72 (s, 3H, cymene Me), 1.16 (m, 6H, CHMe
CDCl
): 171.7 (C¼O), 165.7 (C¼N), 151.4 (Ph), 146.6 (Ph), 139.9 (Ph),
29.3 (Ph), 127.8 (Ph), 127.5 (Ph), 126.9 (Ph), 126.6 (Ph), 121.5 (Ph),
10.3 (Ph), 101.0 (Cipso), 95.4 (Cipso), 94.4 (CH), 87.5 (CH), 85.9 (CH),
4.6 (CH), 55.2 (OMe), 30.5 (CH), 23.9 (Me), 23.7 (Me), 20.6 (Me),
30ClNO Ru (537.06): C, 60.38; H,
.63; N, 2.61. Found: C, 59.28; H, 5.88; N, 2.75%.
2
). C NMR
3
8.4 (Me). Anal. Calcd. for C27
H
2
4
.2.3. Synthesis of {Ru(
h
6-cymene)[L
Similar procedure as for synthesizing compound 1 was adopted.
3
)]Cl} (3)
6
L
3
H (0.30 g, 0.93 mmol), n-BuLi (0.41 mL, 1.0 mmol), and [Ru(
cymene)Cl (0.23 g, 0.47 mmol) were used. Compound 3 was
isolated in 52.4% yield (0.29 g). H NMR (CDCl
Ph), 7.32e7.14 (m, 6H, Ph), 5.48 (s, 1H, CCHC), 5.35 (br, 2H, C
h -
Scheme 3. Amination of benzyl alcohol with primary amines catalyzed by ruthenium
compounds.
2 2
]
1
3
): 7.86e7.85 (m, 2H,
),
), 3.89
),
6 4
H
3
3
4
.92 (d,
JHH ¼ 8 Hz,1H, C
6
H
4
), 4.18 (d,
), 3.24 (sept, JHH ¼ 7 Hz, 1H, CHMe
J
HH ¼ 8 Hz, 1H, C
6 4
H
bidentate ligands also allowed a spin-saturation transfer mecha-
nism in our cymene-ruthenium system. Further explorations are
being conducted with Ru derivatives prepared from these ruthe-
nium compounds and their different catalytic approaches, as well
as their potential efficacy in inhibiting cancer cells.
3
3
(
2
sept, JHH ¼ 7 Hz, 1H, CHMe
2
2
3
.89 (sept, JHH ¼ 7 Hz, 1H, CHMe
2
), 1.77 (s, 3H, cymene Me), 1.71 (s,
13
3
H, Me), 1.37 (m, 12H, CHMe
2
2
), 1.07 (m, 6H, CHMe ). C NMR
(
1
CDCl
3
): 172.4 (C¼O), 167.2 (C¼N), 151.3 (Ph), 143.8 (Ph), 141.8 (Ph),
29.2 (Ph), 138.0 (Ph), 129.5 (Ph), 129.1 (Ph), 128.3 (Ph), 127.9 (Ph),
127.0 (Ph), 126.5 (Ph), 125.4 (Ph), 125.1 (Ph), 123.5 (Ph), 104.3 (Cipso),
4
. Experimental
96.0 (CH), 95.3 (Cipso), 86.8 (CH), 84.2 (CH), 82.1 (CH), 30.5 (CH), 28.1
(
Me), 27.5 (Me), 26.0 (Me), 25.4 (Me), 25.3 (Me), 25.1 (Me), 23.3 (Me),
21.8 (Me), 17.8 (Me). Anal. Calcd. for 40ClNORu
591.20)þ(C 0.2: C, 65.81; H, 6.88; N, 2.30. Found: C, 66.19; H,
6.93; N, 2.35%. Small amount of solvent in the molecules.
4
.1. General procedure
32
C H
(
7 8
H )
All starting materials were used as purchased. H and 13C NMR
1

C.-M. Hsiao et al. / Journal of Organometallic Chemistry 861 (2018) 10e16
15
Table 3
Catalytic amination of benzyl alcohol using amine, base, and Ru(II) complexes 1e5..
Entry
Cat.
base
Time (hr)
Conv (%)
2 2 2
PhC ¼ NCH Ph:NH(CH Ph)
1
2
3
4
5
6
7
8
9
-
-
t-BuOK
KOH
24
24
24
12
24
24
24
24
24
24
trace
8
e
100:0
100:0
100:0
100:0
100:0
100:0
73:27
100:0
84:16
1
1
1
1
2
3
4
5
e
10
25
56
99
99
70
17
64
t-BuOK
t-BuOK
KOH
KOH
KOH
KOH
KOH
1
0
Entry
Cat.
base
Time (hr)
Conv.%
PhCH ¼ NPh: PhCH
2
NHPh
11
12
13
14
15
16
17
-
KOH
t-BuOK
KOH
KOH
KOH
KOH
KOH
24
24
24
24
24
24
24
8
100:0
100:0
100:0
100:0
74:26
50:50
87:13
1
1
2
3
4
5
44
66
99
73
99
71
4
.2.4. Synthesis of [Ru(
Similar procedure as for synthesizing compound 1 was applied.
H (0.20 g, 0.95 mmol), n-BuLi (0.42 mL, 1.1 mmol), and [Ru(
h
6-cymene)(L
4
)Cl] (4)
131.7 (Ph), 130.9 (Ph), 130.7 (Ph), 130.4 (Ph), 129.5 (Ph), 127.9 (Ph),
127.0 (Ph), 125.8 (Ph), 123.4 (Ph), 120.5 (Ph), 115.6 (Ph), 114.8 (Ph),
101.1 (Cipso), 100.2 (Cipso), 86.7 (CH), 81.9 (CH), 80.6 (CH), 79.3 (CH),
30.9 (CH), 22.5 (Me), 22.1 (Me), 19.1 (Me).
6
L
4
h -
cymene)Cl
isolated in 42.0% yield (0.19 g). H NMR (CDCl
.15 (m, 2H, Ph), 7.35e6.94 (m, 5H, Ph), 6.40 (m, 1H, Ph), 5.33 (d,
2 2
]
(0.29 g, 0.48 mmol) were used. Compound 4 was
1
3
): 9.06 (s, 1H, N¼CH),
), 4.65 (d,
8
4.3. General procedure for amination of alcohols
3
3
J
J
HH ¼ 8 Hz, 1H, C
6
H
4
), 5.07 (d,
J
HH ¼ 8 Hz, 1H, C
6 4
H
3
), 4.47 (d, 3JHH ¼ 8 Hz, 1H, C
HH ¼ 8 Hz, 1H, C
6
H
4
6 4
H ), 2.58 (sept,
A flask was charged with Ru compounds (1 mol%), base
3JHH ¼ 7 Hz, 1H, CHMe
), 2.46 (s, 3H, Me), 2.21 (s, 3H, cymene Me),
2
(
1 mmol), alcohols (1 mmol), amines (1 mmol) and toluene (4 mL).
.06 (d, 3
JHH ¼ 7 Hz, 6H, CHMe
). C NMR (CDCl
13
): 168.9 (C¼N),
1
2
3
ꢁ
The solution was heated at 110 C under nitrogen. The volatiles was
then removed under vacuum and the residues were characterized
by 1 H NMR spectroscopy.
1
1
1
3
59.0 (Ph), 141.3 (Ph), 138.2 (Ph), 134.5 (Ph), 130.8 (Ph), 130.3 (Ph),
29.2 (Ph), 128.3 (Ph), 125.4 (Ph), 120.2 (Ph), 115.3 (Ph), 114.4 (Ph),
01.3 (Cipso), 100.5 (Cipso), 85.3 (CH), 82.6 (CH), 81.8 (CH), 80.2 (CH),
1.0 (CH), 22.5 (Me), 22.0 (Me), 21.8 (Me), 19.0 (Me). Anal. Calcd. for
0.2: C, 61.09; H, 5.57; N, 2.81. Found:
C
24
H26ClNORu (481.0) þ (C
H
7 8
)
4.4. X-ray crystallography [12b]
C, 61.74; H, 5.75; N, 3.08%. The product still contains small amount
of toluene after long time vacuum drying.
Suitable crystals of compounds 1e5 were attached to a fine glass
fiber with paratone oil and mounted on goniostat for data collec-
tion. Data collections were performed at 150 K under liquid nitro-
gen vapor for all complexes. Data were collected on a Bruker SMART
4
.2.5. Synthesis of [Ru(
A flask charged with L
.2 mmol) and 15 mL of methanol was stirred for 30 min. The
resulting solution was added to a methanol (10 mL) solution of
h
6-cymene)(L
H (0.20 g, 0.81 mmol), NaOMe (0.07 g,
5
)Cl] (5)
5
1
CCD diffractometer with graphite monochromated Mo-K
tion. No significant crystal decay was found. Data were corrected for
absorption empirically by means of scans. All non-hydrogen
a
radia-
6
[Ru(
h
-cymene)Cl
2
]
2
(0.25 g, 0.41 mmol) at room temperature. The
j
solution was stirred for another hour and filtered through filter
paper to remove sodium chloride. Filtrate was vacuum dried and
residue was recrystallized from a saturated methylene chloride
solution at ꢀ20 C to give red crystals of 5 in 41.0% yield (0.17 g). H
atoms were refined with anisotropic displacement parameters.
For all the structures, the hydrogen atom positions were calculated
and they were constrained to idealized geometries and treated as
riding where the H atom displacement parameter was calculated
from the equivalent isotropic displacement parameter of the bound
atom. An absorption correction was performed with the program
SADABS [27] and the structures of the complexes were solved by
direct methods procedures in SHELXS [28] and refined by full-
ꢁ
1
NMR (CDCl
3
): 9.52 (s, 1H, N¼CH), 8.72 (m, 1H, Ph), 8.02e7.66 (m,
6
5
H, Ph), 7.50 (m, 1H, Ph), 7.03e6.95 (m, 2H, Ph), 6.47 (m, 1H, Ph),
3
3
.33 (d, JHH ¼ 8 Hz, 1H, C
6
H
4
), 5.00 (d, JHH ¼ 8 Hz, 1H, C
6 4
H ), 4.49
H ), 2.53 (sept,
6 4
3
3
(
d, JHH ¼ 8 Hz, 1H, C
6
H
4
), 3.79 (d, JHH ¼ 8 Hz, 1H, C
3
2
J
HH ¼ 7 Hz, 1H, CHMe
2
), 2.08 (s, 3H, cymene Me), 1.03 (d,
matrix least-squares methods, on F 's, in SHELXL [29]. All the
relevant crystallographic data and structure refinement parameters
are summarized in Table 2.
3JHH ¼ 7 Hz, 3H, CHMe
), 0.96 (d, JHH ¼ 7 Hz, 3H, CHMe
3
13
2
2
). C NMR
(
CDCl
3
): 169.1 (C¼N), 157.6 (Ph), 137.6 (Ph), 135.3 (Ph), 132.8 (Ph),

16
C.-M. Hsiao et al. / Journal of Organometallic Chemistry 861 (2018) 10e16
Acknowledgements
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J.-H. Huang, Eur. J. Inorg. Chem. (2004) 4898;
The authors express their appreciation to the Ministry of Science
and Technology of Taiwan (MOST 105-2113-M-018-005) for finan-
cial assistance. We also thank the National Changhua University of
Education for providing the facility of X-ray diffractometer and
NMR spectrometer and the National Center for High-performance
Computing for supporting the CCDC database searching.
(
e) S.-H. Hsu, J.-C. Chang, C.-L. Lai, C.-H. Hu, H.M. Lee, G.-H. Lee, S.-M. Peng, J.-
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