Transition Metal Chemistry
enantioselective catalysts [29]. It was discussed that the
lytic cycle where the hydride on ruthenium and proton on
nitrogen attack the polar bond [30].
analysis (Calculated for C19H27NCl2Ru): C: 51.70, H: 6.17;
N: 3.17; Found: C: 51.22, H: 6.02, N: 3.02, 1H-NMR: 1.13
(6H, d, C(CH3)2 aniline), 1.20 (6H, d, C(CH3)2 p-cymene),
2.09 (3H, s, Ph–CH3 p-cymene), 2.71 (1H, septet, CH(CH3)2
p-cymene), 2.84 (1H, septet, CH(CH3)2 p-cymene), 4.88
(2H, s, NH2 aniline) 5,79 (4H, d, CH p-cymene), 6.50 (2H,
d, CH aniline), 6.87 (2H, d, CH aniline). FT-IR (cm−1):
3203, 3104, 2953, 2865, 1608, 1600, 1505, 1465, 1378,
1230, 1119, 1053,1005, 882, 839, 568.
Due to the importance of the primary amine group in
the catalytic transfer hydrogenation of ketones, we prepared
four half-sandwich Ru(II) complexes (1)-(4) derived from
[Ru(η6-p-cymene)Cl2]2 and p-substituted aniline derivatives
with the general formulae [Ru(η6-p-cymene)(L)Cl2] (where
L is p-methyl, p-isopropyl, p-methoxy, or p-hydroxy ani-
line) and used as catalysts for the transfer hydrogenation
of ketones. The complexes were characterized by FT-IR,
UV–Vis. and 1H-NMR spectroscopies, and the structures of
(2)–(4) were determined by X-ray crystallography.
[Ru(η6-p-cymene)(p-methoxyaniline)Cl2] (3): Yield:
87%, Colour: Red, M.p. 199 °C (decomposed), Elemental
analysis (Calculated for C17H23NOCl2Ru): C: 47.56, H: 5.40;
N: 3.26; Found: C: 47.31, H: 5.12, N: 3.01, 1H-NMR: 1.19
(6H, d, C(CH3)2 p-cymene), 2.09 (3H, s, Ph–CH3 p-cymene),
2.84 (1H, septet, CH(CH3)2 p-cymene), 3.62 (3H, s, OCH3),
4.75 (2H, s, NH2), 5.81 (4H, d, CH p-cymene), 6.64 (2H, d,
CH aniline), 6.66 (2H, d, CH aniline). FT-IR (cm−1): 3283,
3810, 3100, 2947, 1596, 1579, 1510, 1453, 1305, 1247,
1167, 1096, 1024, 876, 827, 736, 544.
Experimental
Starting materials [Ru(η6-p-cymene)Cl2]2, p-methylaniline,
p-isopropyl aniline, p-methoxy aniline, and p-hydroxyl ani-
line were purchased from commercial sources and used as
received. FT-IR spectra of the complexes recorded taken on
a PerkinElmer Spectrum 100 FT-IR, and FT-IR spectra are
given in the supplementary documents (Figs. S1–S4). The
UV–Vis. absorption spectra were recorded on a PerkinElmer
Lambda 45 spectrophotometer. 1H-NMR spectra were meas-
ured on Bruker Avance III 400 MHz spectrometer using
d6-DMSO as solvent. Catalytic conversion of ketones to
alcohols was monitored by GC using a YL6500 Instrument.
[Ru(η6-p-cymene)(p-hydroxyaniline)Cl2] (4): Yield: 85%,
Colour: Red, M.p.: 195 °C (decomposed), Elemental analy-
sis (Calculated for C16H21NOCl2Ru): C: 46.27, H: 5.10; N:
3.37; Found: C: 46.05, H: 4.95, N: 3.12, 1H-NMR: 1.20 (6H,
d, C(CH3)2 p-cymene), 2.09 (3H, s, Ph–CH3 p-cymene), 2.82
(1H, septet, CH(CH3)2 p-cymene),4.43(2H, s, NH2 aniline),
5.81 (4H, d, CH p-cymene), 6.41–6.43(4H, d, CH aniline),
8.34 (1H, b, OH aniline). FT-IR (cm−1): 3341, 3255, 3187,
3101, 2960, 1612, 1600, 1569, 1501, 1511, 1458, 1375,
1357, 1255, 1214, 1119, 834, 803, 759, 663,573, 542.
X‐ray crystallography
Synthesis of the complexes
X‐ray crystallographic data for complexes (2)-(4) were col-
lected at 293 (2) K on a Bruker D8 QUEST difractometer
using Mo‐Kα radiation (λ = 0.71073 Å). Data reduction
was performed using Bruker SAINT [31, 32]. SHELXT
the structures [33, 34]. The structures were solved by direct
methods and refned on F2 using all the refections. All the
non‐hydrogen atoms were refned using anisotropic atomic
displacement parameters, and hydrogen atoms bonded to
carbon, nitrogen, and oxygen atoms were inserted at calcu-
lated positions using a riding model and refned with tem-
perature factors. The crystal data and refnement details are
given in Table 1. Hydrogen bond parameters are given in the
supplementary fle (Tables S1–S3).
The para-substituted aniline derivative (0.326 mmol) in etha-
nol (5 mL) was added dropwise to a refuxing solution of
[Ru(η6-p-cymene)Cl2]2 (100 mg, 0.16 mmol) in ethanol (15
mL). The reaction solutions were refuxed for 24 h. Upon
cooling to 298 K, the solvent volume was reduced to 5 mL.
Red crystals formed in three days and were fltered and dried
in air.
[Ru(η6-p-cymene)(p-methylaniline)Cl2] (1): Yield:
84%, Colour: Red, M.p.: 229 °C (decomposed), Elemen-
tal analysis (Calculated for C17H23NCl2Ru): C: 49.40, H:
5.61; N: 3.39; Found: C: 49.18, H: 5.42, N: 3.11, 1H-NMR:
1.21 (6H, d, C(CH3)2 p-cymene), 2.10 (3H, s, Ph–CH3
p-cymene), 2.12 (3H, s, Ph–CH3 aniline), 2.83 (1H, septet,
CH(CH3)2 p-cymene), 4.84 (2H, s, NH2 aniline), 5.82 (4H,
d, CH p-cymene), 6.48 (2H, d, (CH aniline), 6.83 (2H, d,
(CH aniline), FT-IR (cm−1): 3323, 3200, 3120, 3040, 2956,
2861 1610, 1578, 1515, 1467, 1375, 1225, 1135, 1105,1086,
1049, 876, 819, 7450, 668, 546, 450.
Transfer hydrogenation of ketones
The acetophenone derivative (1 mmol) was dissolved in in
2-propanol (9.4 mL) followed by addition of base and cata-
lyst (5 mg). The reaction mixture was stirred at 82 °C. Sam-
ples from the reaction solution were collected periodically,
[Ru(η6-p-cymene)(p-isopropylaniline)Cl2] (2): Yield
82%, Colour: Red, M.p. 199 °C (decomposed), Elemental
1 3