Asymmetric hydrogenation of aromatic ketones in ionic-liquid media catalyzed by Ru-TPPTS-(1S,2S)-DPENDS complexes

Article abstract of DOI:10.1016/j.tetasy.2005.03.037

The catalytic performance of ruthenium phosphine complexes using (1S,2S)-DPENDS [(1S,2S)-1,2-diphenyl-1,2-ethylene diamine sulfonate disodium] as a chiral modifier in the asymmetric hydrogenation of aromatic ketones was examined in a series of hydrophilic

Full text of DOI:10.1016/j.tetasy.2005.03.037

Tetrahedron:
Asymmetry
Tetrahedron: Asymmetry 16 (2005) 1959–1962
Asymmetric hydrogenation of aromatic ketones in ionic-liquid
media catalyzed by Ru-TPPTS–(1S,2S)-DPENDS complexes
a,b
a
a
a
a
Wei Xiong, Qi Lin, Hongxia Ma, Hongjie Zheng, Hua Chen and Xianjun Li
a,
*
a
Key Lab of Green Chemistry and Technology, Ministry of Education, The Institute of Homogeneous Catalysis,
Department of Chemistry, Sichuan University, No. 29 Wangjiang Road, Chengdu, Sichuan 610064, PR China
b
Department of Chemistry, Xichang College, Xichang 615022, PR China
Received 5 March 2005; accepted 30 March 2005
Abstract—The catalytic performance of ruthenium phosphine complexes using (1S,2S)-DPENDS [(1S,2S)-1,2-diphenyl-1,2-ethylene
diamine sulfonate disodium] as a chiral modifier in the asymmetric hydrogenation of aromatic ketones was examined in a series of
+
hydrophilic ionic liquids [RMIM] [p-CH C H SO ] (R = ethyl, butyl, octyl, dodecyl). The synergistic effect between (1S,2S)-
ꢀ
3
6
4
3
DPENDS and KOH significantly accelerated the reaction and enhanced the enantioselectivity. An ee value of 84.8% was obtained
in the asymmetric hydrogenation of acetophenone under the optimized conditions. The products were conveniently separated with
cyclohexane extraction, and both the ruthenium catalyst and (1S,2S)-DPENDS were kept in the ionic liquid and could be reused.
ꢀ
2005 Elsevier Ltd. All rights reserved.
1
. Introduction
stable chiral catalyst, as well as better combinations of
ILs and metal complexes, we synthesized a series of ionic
+
ꢀ
liquids [RMIM] [p-CH C H SO ] and studied the
3 6 4 3
Catalytic asymmetric hydrogenation is a powerful
method for the synthesis of enantiomerically pure com-
pounds. A lot of catalysts contain rhodium and ruthe-
nium complexes using chiral phosphines and amines as
ligands display excellent performances in the asymmet-
ric homogeneous hydrogenation of prochiral ketones
catalytic performance of a novel catalyst system
[RuCl (TPPTS) ] –(1S,2S)-DPENDS–KOH [(TPPTS:
2
2 2
P(m-C H SO Na) ) in the asymmetric hydrogenation
3
6
4
3
of aromatic ketones in the ionic liquids.
1
and other carbonyl compounds. However, their practi-
cal applications are often limited owing to the high cost
of the chiral ligand and noble metal, as well as the diffi-
culty in the separation of products from chiral catalyst.
The immobilization of a homogeneous catalyst provides
an efficient approach to resolve the problem. Recently
room temperature ionic liquids (RTILs) have been used
as an alternative reaction media in asymmetric hydro-
2
. Results and discussion
2
.1. Influence of ionic liquid properties and temperature
The data listed in Table 1 indicate that the activities of
the catalyst system [RuCl (TPPTS) ] –(1S,2S)-
DPENDS–KOH were high in the ionic liquids contain-
2
2 2
2
3
4
genation of enamides, arylacrylic acids, imines,
6–8
ꢀ
ing the anionic group [p-CH C H SO ] and BF , but
3 6 4 3
ꢀ
5
aromatic ketones and b-ketoesters.
These reports
4
when butyl group in imidazole was substituted by
another alkyl group, the enantioselectivities decreased
gradually with an increase of alkyl chain length. The
results suggest that increasing the hydrophobic chain
length in imidazole could be unfavourable for the
formation of the (R)-configuration in the transition state
of hydrogenation of acetophenone. The activity of the
indicated that the products of hydrogenation could be
easily separated from the catalyst by decantation or
extraction with organic solvents while the chiral catalyst
in ionic liquid (IL) could be reused several times without
obvious decrease in the activity and enantioselectivity.
However the chiral phosphines were expensive and too
sensitive to air. In order to develop an inexpensive and
þ
ꢀ
catalyst system significantly decreased in ½BMIMꢁ PF .
6
þ
ꢀ
The conversion of acetophenone in ½BMIMꢁ PF was
6
only 5.6% for 1 h. As [RuCl (TPPTS) ] is a strong
hydrophilic complex and its solubility in hydrophobic
*
Corresponding author. Tel./fax: +86 28 85412904; e-mail: scuulixj@
mail.sc.cninfo.net
2
2 2
0
957-4166/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2005.03.037

1960
W. Xiong et al. / Tetrahedron: Asymmetry 16 (2005) 1959–1962
Table 1. Influence of different ionic liquid media on asymmetric
hydrogenation
Table 3. Influence of KOH concentration on asymmetric hydro-
genation
ꢀ
2
Ionic liquid
Conv. (%) ee (%) Configuration
[KOH] · 10 mol/L
Conv. (%)
ee (%)
þ
þ
ꢀ
½
½
½
½
½
½
EMIMꢁ ½p-CH3C6H4SO ꢁ
100
100
100
75.2
79.2
66.5
59.4
67.1
52.9
R
R
R
R
R
R
0.0
4.5
0.60
97.0
99.0
99.8
100
44.2
72.5
73.8
75.6
79.2
77.7
3
ꢀ
BMIMꢁ ½p-CH3C6H4SO ꢁ
3
þ
ꢀ
OMIMꢁ ½p-CH3C6H4SO ꢁ
9.0
3
þ
ꢀ
DoMIMꢁ ½p-CH3C6H4SO ꢁ 100
18.0
36.0
39.0
3
þ
ꢀ
ꢀ
a
BMIMꢁ BF
98.5
5.6
4
þ
a
BMIMꢁ PF
100
6
+
The reaction conditions in [BMIM] [p-CH
ꢀ
media are the
Reaction conditions: acetophenone: 0.85 mmol, Ru complex/acetophe-
none/(1S,2S)-DPENDS = 1:112:6 (mole ratio), [KOH] = 0.36 mol/L,
ionic liquid: 1.0 mL, PH2 = 5 MPa, Temp: 50 ꢁC, reaction time: 0.5 h.
3
C
6
H
4
SO
3
]
same as in Table 1.
a
Reaction time: 1.0 h.
Table 4. Influence of (1S,2S)-DPENDS concentration on asymmetric
hydrogenation
þ
ꢀ
½
BMIMꢁ PF is very low, the catalyst can not fully exert
6
its function. The matching property between metal com-
plexes and ionic liquids not only influences the solubility
of metal complexes in ionic liquids, but also influences
the catalytic activity. When both are matching, the cata-
lyst system will display high activity, in addition to the
character being favourable for the separation of metal
complex catalyst from products.
ꢀ2
[
(1S,2S)-DPENDS] · 10 mol/L
Conv. (%)
ee (%)
0
0
1
2
3
.0
1.1
23.3
48.9
62.9
82.6
100
0.0
60.1
61.3
71.3
76.1
79.2
78.9
.48
.9
.4
.8
4.8
.0
6
100
The results listed in Table 2 suggested that the enantio-
selectivity increased with a decrease of reaction temper-
ature with an ee value of 84.8% being obtained at 5 ꢁC.
+
The reaction conditions in [BMIM] [p-CH
ꢀ
3
SO ] media are the
3
C
6
H
4
same as in Table 1.
tion process and promotes the catalyst precursor
[
RuCl (TPPTS) ] to convert into active species
2 2 2
Table 2. Effect of reaction temperature on asymmetric hydrogenation
1
[
RuHCl(TPPTS) –DPENDS] as described. However,
2
Temperature Reaction Conv. (%) ee (%) Configuration
(
the enhancement role of KOH for the enantioselectivity
and the synergistic effect was not observed in homoge-
neous catalysis. This suggests that the catalytic mecha-
nism is different from that reported by Noyori et al.
and is currently being studied.
ꢁC)
time (h)
5
1
2
5
2.0
2.0
2.0
0.5
31.8
48.5
84.8
83.0
81.3
79.2
R
R
R
R
ꢀ
1
,18
5
0
0
100
100
+
The reaction conditions in [BMIM] [p-CH
C
6
H
4
SO
3
]
media are the
2.3. Influence of different ruthenium complexes
3
same as in Table 1, except for a change in temperature.
The activities and enantioselectivities of different ruthe-
nium complexes in the asymmetric hydrogenation of
acetophenone were investigated in [BMIM] -
2.2. Influence of (1S,2S)-DPENDS and KOH
concentration
+
ꢀ
[
in Table 5. The data showed that the [RuCl (TPPTS) ]
p-CH C H SO ] solution with the results summarized
3
6
4
3
2
2 2
The influence of (1S,2S)-DPENDS and KOH concen-
tration on the asymmetric hydrogenation of acetophe-
none is very significant as shown in Tables 3 and 4.
The conversion of acetophenone was only 1.1% with
an ee value of zero in the absence of (1S,2S)-DPENDS.
The addition of both (1S,2S)-DPENDS and KOH
greatly enhanced the catalytic activity and enantioselec-
tivity. When the concentrations of (1S,2S)-DPENDS
and KOH were 4.8 · 10 mol/L and 0.36 mol/L, the
conversion and ee value could reach 100% and 79.2%,
respectively. However, if there was no addition of
KOH into the reaction solution, the conversion was only
was the most efficient catalyst precursor. The conversion
of acetophenone and the ee value of the products were
1
00% and 79.2% for 0.5 h, respectively. When phosphine
ligand TPPTS was used instead of other water-soluble
diphosphine ligand BISBIS, the activities and enantio-
selectivities obviously decreased, because the stability and
steric effect of chelate ruthenium complex, which was
formed by BISBIS coordination with Ru, would influ-
ence the catalytic activity and chiral modification of
ꢀ2
Table 5. Influence of different ruthenium complexes
0
.6%. The results suggest that the combination of chiral
Ruthenium complex
[RuCl (TPPTS) ]
Conv. (%)
ee (%)
diamine and KOH is an essential factor for the forma-
tion of a chiral induction and the active catalytic species.
This synergistic effect between the chiral diamine and
KOH was also found in our research on the asymmetric
hydrogenation of acetophenone using c-Al O sup-
2
2 2
100
39.2
3.0
79.2
58.6
53.1
33.3
RuCl
RuCl
RuCl
2 2
(BISBIS)
3
–2TPPTS
2
(COD)–2TPPTS
6.8
2
3
1
7
ported ruthenium nanocluster catalyst. The important
The reaction conditions are the same as in Table 1, except the ionic
+
liquid is [BMIM] [p-CH C H SO ] .
ꢀ
role of KOH is to neutralize HCl formed in the activa-
3 6 4 3

W. Xiong et al. / Tetrahedron: Asymmetry 16 (2005) 1959–1962
1961
(
1S,2S)-DPENDS. When the catalyst precursor was
RuCl , the ruthenium must be reduced to a low oxida-
Table 7. Recycling and reuse of [RuCl
ꢀ
2
(TPPTS)
2
]
2
catalyst in ionic
+
liquid [BMIM] [p-CH
3
C
6
H
4
SO
3
]
3
tion state and coordinated with TPPTS, in order for
the ruthenium complex to become an active catalyst.
COD in RuCl (COD) would be exchanged with TPPTS
Run
Conv. (%)
ee (%)
1
2
3
4
5
6
7
100
100
79.2
74.2
71.6
70.3
70.3
69.3
70.8
72.6
69.1
2
in the solution according to the reaction:
96.4
98.1
97.4
88.0
68.7
94.0
91.2
RuCl (COD) + 2TPPTS ! RuCl (TPPTS) + COD
2
2
2
then the ruthenium complex was able to dissolve in
[
lyst precursors RuCl and RuCl (COD) were used in the
+
BMIM] [p-CH C H SO ] . Therefore, when both cata-
ꢀ
a
3
6
4
3
8
9
3
2
reaction, there was a long induction period for forming
catalytic active species, causing the very low catalytic
activities observed.
The reaction conditions are the same as in Table 1.
a
ꢀ4
1
.8 · 10 mol of KOH is added in the eighth run.
3. Conclusions
2
.4. Hydrogenation of different aromatic ketones
[
system in ionic liquid [BMIM] [p-CH C H SO ]
RuCl (TPPTS) ] –(1S,2S)-DPENDS–KOH
catalyst
2
2 2
Asymmetric hydrogenation of different aromatic ke-
tones in [BMIM] [p-CH C H SO ] were carried out
+
ꢀ
+
ꢀ
3
3
6
4
3
3
6
4
exhibits excellent catalytic properties for asymmetric
hydrogenation of acetophenone. A synergistic effect be-
tween (1S,2S)-DPENDS and KOH in ionic liquid solu-
tion significantly accelerates the reaction and enhances
the enantioselectivity. The ionic liquid phase containing
the active catalyst and chiral ligand can be reused for
several times without significant decrease in activity
and ee value.
under the same reaction conditions with the results sum-
marized in Table 6. Acetophenone and propiophenone
exhibited the highest reactivities, and ee values of their
hydrogenation products also were higher than those of
other ketones. The substituent in the phenyl ring,
whether it was an electron-withdrawing group or elec-
tron-donating group, had an obvious influence on the
reactivity of aromatic ketones. The decrease in reaction
rates and ee values can be mainly attributed to the steric
effect, which influences the reactant–modifier interac-
tion. The major product in the hydrogenation of
4. Experimental
2
ethanol. The change in configuration is agreement with
that observed in the literature.
-methoxy-acetophenone was (S)-2-methoxy-a-phenyl
4
.1. Materials and methods
1
9
1-Methylimidazole (Fluka, >99%) and 1-butanebromide
(
Lancaster, >99%) were distilled before use. Aromatic
Table 6. Hydrogenation of different aromatic ketones
ketones (P98% Acros) RuCl (COD) [dichloro(1,5-
2
Substrate
Conv. (%)
ee (%)
R/S
cyclooctadiene)ruthenium(II), 99%] (Strem Chemical
Co.) and hydrogen (99.99%) were used as received.
Hexafluorophosphoric acid (Acros, 60 wt % solution in
water), p-toluene sulfonic acid, RuCl Æ3H O and
Acetophenone
Propiophenone
100
100
79.2
80.6
46.4
63.7
66.3
57.3
51.8
40.0
64.7
R
R
R
R
R
R
R
S
2
2
2
2
4
2
4
-Fluoroacetophenone
-Chloroacetophenone
-Bromoacetophenone
98.2
96.4
86.5
88.6
78.3
68.0
83.0
3
2
other reagents are analytical grade. TPPTS, BISBIS
(sodium of sulfonated 2,2 -bis(diphenylphosphino-
methyl)-1,1 -biphenyl) and a series of ionic liquids
0
-(Trifluoromethyl)acetophenone
-(Trifluoromethyl)acetophenone
-Methoxyacetophenone
-Methoxyacetophenone
0
þ
ꢀ
½
RMIMꢁ ½p-CH
3
C
dodecyl) (Scheme 1) were synthesized according to
6
H
4
SO ꢁ (R = ethyl, butyl, octyl,
3
R
9
–14
known methods in our laboratory.
[RuCl (TPPTS) ]
2 2 2
The reaction conditions are the same as in Table 1.
2
.5. Catalyst recycling
+
-
[
p-CH C H SO ]
3 6 4 3
N
N
We have demonstrated that the products could be sepa-
rated by extraction with cyclohexane and the ionic
liquid phase containing the active catalyst while the
chiral ligand could be reused several times in the asym-
metric hydrogenation of acetophenone. The results are
listed in Table 7. Although the activities of the catalyst
system [RuCl (TPPTS) ] –(1S,2S)-DPENDS–KOH de-
H C
R
3
R= C H , C H , C H17, C12H25
2
5
4
9
8
Scheme 1. Ionic liquids.
2
2 2
creased in runs 6 and 7, the ee values could still be main-
ꢀ4
tained at about 70%. When 1.8 · 10 mol KOH was
supplied into the ionic liquid solution, the conversion
rose from 68.7% (run 7) to 94.0% (run 8). These results
further confirm the important effect of KOH on the
reaction.
NaO3S
SO Na
3
H N
2
NH2
Scheme 2. (1S,2S)-DPENDS.

1962
W. Xiong et al. / Tetrahedron: Asymmetry 16 (2005) 1959–1962
O
OH
[
RuCl (TPPTS) ] -(1S,2S)-DPENDS
2 2 2
+
H
2
Ar
R
*
Ar
R
Ionic liquids, KOH
Ar = C H , o-FC H , o-ClC H , o-BrC H , o-CF C H , o-CH OC H , p-CF C H , p-CH OC H , R = CH
3
6
5
6
4
6
4
6
4
3
6
4
3
6
4
3
6
4
3
6
4
Ar =C H , R = C H
2 5
6
5
Scheme 3. The asymmetric hydrogenation of aromatic ketones.
and RuCl (BISBIS) were prepared by a ligand exchange
2
A.; Pollet, P.; Mckoon, E.; Liotta, C. L.; Jessop, P. G. J.
Am. Chem. Soc. 2001, 123, 1254.
. Giernoth, R.; Krumm, M. S. Adv. Synth. Catal. 2004, 346,
989.
. Zhu, Y. H.; Carpenter, K.; Ching, C. B.; Bahnmueller, S.;
Chan, P. K. Angew. Chem., Int. Ed. 2003, 42, 3792.
. Ngo, H. L.; Hu, A.; Lin, W. B. Chem. Commun. 2003,
2
5
1
method. (1S,2S)-DPENDS (Scheme 2) was prepared
by means of sulfonation of (1S,2S)-DPEN (Chengdu
4
5
6
7
9
,16
LiKai Chiral Tech Co., >99%).
4
.2. Hydrogenation of aromatic ketones
1
912.
The reaction was performed in a 60 mL stainless auto-
clave with a glass linear and magnetic stirrer. A typical
procedure for an asymmetric hydrogenation of aromatic
ketones (Scheme 3) is as follows: the ruthenium com-
plexes, (1S,2S)-DPENDS, KOH, ionic liquid and reac-
tant were added to autoclave, followed by a purge
with hydrogen, three times. Hydrogen was introduced
to the desired hydrogen pressure. The products were ex-
tracted by cyclohexane and analyzed by GC-960 with
. Hu, A.; Ngo, H. L.; Lin, W. B. Angew. Chem., Int. Ed.
2004, 43, 2501.
8. Berthod, M.; Joerger, J. M.; Mignani, G.; Vaultier, M.;
Lemaire, M. Tetrahedron: Asymmetry 2004, 15, 2219.
9
. Chen, H. PhD thesis, Sichuan University, 1999.
0. Tim, T.; Stephen, M. B.; John, C. Tetrahedron Lett. 2000,
1, 4503.
1
1
1
1
4
1. Herrmann, W. A.; Kohlpaintrer, C. W.; Bahrmann, H.;
Konkol, W. J. Mol. Catal. 1992, 73, 191.
2. Fuller, J.; Carlin, R. T.; Delong, H. C.; Haworth, D.
Chem. Commun. 1994, 299.
3. Wilkes, J. S.; Zaworotko, M. J. Chem. Commun. 1992,
965.
14. Bonbote, P.; Dias, A.; Papageorgiou, N.; Kalyansun-
daram, K.; Gratzel, M. Inorg. Chem. 1996, 35, 1168.
5. Face, E.; Santini, C.; Senocq, F.; Basset, J. M. J. Mol.
Catal. 1992, 72, 331.
6. Ma, Y.-P.; Liu, H.; Chen, L.; Cui, X.; Zhu, J.; Deng, J.-G.
Org. Lett. 2003, 5, 2103.
TM
FID detector and b-DEX 120 capillary column
(30 m · 0.25 mm, 0.25 lm film) at 115 ꢁC. The enantio-
meric excess (ee value) was calculated from the equation:
ee (%) = 100 · (R ꢀ S)/(R + S).
1
1
References
1
2
3
. (a) Noyori, R.; Ohkuma, T. Angew. Chem., Int. Ed. 2001,
0, 40; (b) Noyori, R. Adv. Synth. Catal. 2003, 345, 15.
. Guernik, S.; Wolfson, A.; Herskowitz, M.; Greenspoon,
N.; Geresh, S. Chem. Commun. 2001, 2314.
. (a) Berger, A.; de Souza, R. F.; Delgado, M. R.; Dupont,
J. Tetrahedron: Asymmetry 2001, 12, 1825; (b) Brown, R.
17. Huang, Y. Y.; Ma, H. X.; Xiong, W.; Chen, H.; Li, X. J. J.
Chin. Catal. 2004, 25, 962.
18. Somdoval, C. A.; Ohkuma, T.; Muniz, K.; Noyori, R. J.
Am. Chem. Soc. 2003, 125, 13490.
19. Hess, R.; Vargas, A.; Mallat, T.; Burgi, T.; Baiker, A. J.
Catal. 2004, 222, 117.
4