Preparation of microgel-supported chiral catalysts and their application in the asymmetric hydrogenation of aromatic ketones

Article abstract of DOI:10.1016/j.reactfunctpolym.2012.03.011

An enantiomerically pure chiral monomer (S,S)-2 was prepared and copolymerized with styrene and four different cross-linkers to produce four distinct microgel-supported chiral TsDPEN derivatives. These chiral copolymers were allowed to form complexes with

Full text of DOI:10.1016/j.reactfunctpolym.2012.03.011

Reactive & Functional Polymers 72 (2012) 378–382
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Reactive & Functional Polymers
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Preparation of microgel-supported chiral catalysts and their application
in the asymmetric hydrogenation of aromatic ketones
⇑
Jia Deng, Cuifen Lu , Guichun Yang, Zuxing Chen
Ministry-of-Education Key Laboratory for the Green Preparation and Application of Functional Materials, Hubei University, Wuhan 430062, China
School of Chemistry and Chemical Engineering, Hubei University, Wuhan 430062, China
a r t i c l e i n f o
a b s t r a c t
Article history:
An enantiomerically pure chiral monomer (S,S)-2 was prepared and copolymerized with styrene and four
different cross-linkers to produce four distinct microgel-supported chiral TsDPEN derivatives. These chi-
ral copolymers were allowed to form complexes with [RuCl2(cymene)]2 and the resulting homogeneous
catalysts were applied in asymmetric hydrogenation reactions of aromatic ketones to give enantioen-
riched secondary alcohols in quantitative yield. These polymeric catalysts can be easily separated from
the reaction mixture and recycled several times without a significant loss in catalytic activity.
Ó 2012 Elsevier Ltd. All rights reserved.
Received 8 November 2011
Received in revised form 23 March 2012
Accepted 26 March 2012
Available online 2 April 2012
Keywords:
Microgel-supported
TsDPEN
Catalyst
Asymmetric hydrogenation
Aromatic ketones
1. Introduction
catalysts in the literature appear to be more active than Ru–TsDPEN
itself. As a result, chemists have searched for soluble polymers that
Enantioselective transfer hydrogenation reactions of prochiral
ketones have been achieved using a range of catalysts [1–4].
Among the various chiral catalysts reported, the most notable
is the ruthenium catalyst Ru–TsDPEN (TsDPEN = N-(p-toluenesul-
fonyl)-1,2-diphenylethylenediamine) developed by Noyori and
co-workers [5]. This catalyst and related variants provide good to
excellent levels of enantioselectivity when applied in the hydroge-
nation of a wide range of prochiral ketones and imines [6–9]. How-
ever, as with most other homogeneous catalysts, the Noyori
Ru–TsDPEN catalyst cannot be easily separated from the product
of the reaction or recovered for reuse.
The design and synthesis of polymer-supported asymmetric cat-
alysts has progressed with the development of asymmetric cata-
lysts. Polymer-supported catalysts have been used in various
asymmetric reactions mainly because their use facilitates the sepa-
ration of the catalyst from the reaction mixture. In fact, a consider-
able number of papers on the immobilization of chiral catalysts onto
insoluble polymers have been reported [10–15]. Immobilization of a
chiral catalyst onto a solid support often affords good recyclability,
but immobilized chiral catalysts often suffer from decreased cata-
lytic activity and/or enantioselectivity. None of the immobilized
could be used as supports [16–18]. This methodology has been
demonstrated to be a very successful approach that generates
catalysts with the best qualities of insoluble polymer supports
and the advantages of classic solution phase synthesis.
Poly(ethylene glycol) (PEG) and non-cross-linked poly(styrene)
(NCPS) are two of the more frequently used soluble polymer
supports in liquid phase organic synthesis (LPOS) [19,20]. How-
ever, PEG is insoluble at low temperatures in a number of organic
solvents and is unstable if exposed to strong acids or to some orga-
nometallic reagents. NCPS has good solubility characteristics, but
at high concentrations and low temperatures, NCPS solutions
become extremely viscous.
Microgels offer an attractive alternative to soluble supports. This
interesting class of materials is defined as ‘‘intramolecularly cross-
linked molecules that form a stable solution in many solvents’’.
Additionally, microgel solutions exhibit low viscosity even at high
concentrations and low temperatures. Because of their unique prop-
erties microgel solutions seem to be good candidates for use as
soluble supports in organic synthesis. There has been some note-
worthy work in the field of soluble functional polymers toward this
end. Specifically, the pioneering work on microgel-supported
organic synthesis reported by Janda et al. is encouraging [21–23].
Our laboratory has accumulated abundant experience in soluble
polymer-supported synthesis and has synthesized several small
molecule libraries using PEG and NCPS supports [24–26]. In this arti-
cle, we describe the synthesis of a chiral TsDPEN monomer and its
⇑
Corresponding author at: Ministry-of-Education Key Laboratory for the Green
Preparation and Application of Functional Materials, Hubei University, Wuhan
430062, China. Tel.: +86 27 50865322; fax: +86 27 88663043.
E-mail address: lucf@hubu.edu.cn (C. Lu).
1381-5148/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.reactfunctpolym.2012.03.011

J. Deng et al. / Reactive & Functional Polymers 72 (2012) 378–382
379
copolymerization with a styrene monomer and four different cross-
linkers to prepare four microgel-supported chiral TsDPEN copoly-
mers (Scheme 1). Asymmetric hydrogenation reactions of aromatic
ketones using the homogeneous polymeric catalyst prepared from
microgel-supported TsDPEN derivatives are also discussed.
mixtures as the eluent. A UV detector (UVD-3000) was used for
peak detection. GC analyzes of reaction conversion were performed
on a Techcomp GC-7890F containing a capillary column (SE-54,
30 m  0.25 mm). Gel permeation chromatographic analyzes
(GPC) were carried out on a
l-styragel preparative liquid chro-
matograph (China) with a multi angle laser photometer (DAWN
HELEOS II, Wyatt, USA) and a refractive index (RI) detector (Optilab
Rex, Wyatt, USA) using polystyrene standards. Thermogravimetric
analyzes were performed on a Perkin-Elmer TGA 7 thermogravi-
metric analyzer. The weight percentage of Ru was measured using
an IRIS Advantage ER/S inductively coupled plasma-atomic emis-
sion spectroscopy (ICP-AES) analyzer.
2. Experimental
2.1. Materials
N,N-Dimethylformamide (DMF) was freshly distilled from cal-
cium hydride under reduced pressure. Dichloromethane (DCM)
was distilled from P2O5 before use. Tetrahydrofuran (THF) and
toluene were freshly distilled from sodium benzophenone ketyl
before use. All ketones were distilled from calcium hydride under
nitrogen prior to use. Reactions were monitored by TLC using pre-
coated plates of silica gel plates (HF254, 0.5 mm, Yantai, China).
Column chromatography was performed with a silica gel column
(200–300 mesh, Yantai, China).
2.3. Preparation of (1S,2S)-N-(p-toluenesulfonyl)-1,2-
diphenylethylenediamine 2
(S,S)-2 was prepared according to Ref. [27]. Mp: 116–117 °C
(lit.[28]: 116 °C); IR (NaCl) t ;
: 3350, 3338, 3293, 1327, 1155 cmÀ1
1H NMR (600 MHz, CDCl3) d: 4.17 (d, J = 4.2 Hz, 1H, NH2CHA), 4.41
(d, J = 4.2 Hz, 1H, NHCHA), 5.38 (d, J = 10.8 Hz, 1H,=CH), 5.80 (d,
J = 16.8 Hz, 1H,=CH), 6.66 (dd, J = 10.8, 17.4 Hz, 1H,=CH), 7.15 (m,
12H, Ar–H), 7.36 (d, J = 7.8 Hz, 2H, SO2Ar–H); 13C NMR (150 MHz,
CDCl3) d: 59.2, 62.8, 115.2, 126.2, 126.6, 127.0, 127.2, 127.4, 127.8,
128.2, 128.4, 134.8, 139.1, 139.5, 141.5, 142.3.
2.2. Measurements
1H NMR (600 MHz) and 13C NMR (150 MHz) spectra were re-
corded on a Varian Unity INOVA 600 spectrometer in CDCl3 using
TMS as an internal standard. Coupling constants are recorded in
Hz. Melting points were determined on a WRS-1A digital melting
point apparatus and are uncorrected. IR spectra were recorded on
a Perkin-Elmer IR-spectrum one spectrometer. Elemental analyzes
were performed on a Vario EL III (Germany) analyzer. HPLC ana-
lyzes were performed on a Dionex UltiMate 3000 equipped with
a chiral column (Chiralcel OD, Daicel) using hexane/2-propanol
2.4. General procedure for the preparation of microgel-supported
chiral TsDPEN 4
A mixture of (S,S)-2 (0.38 g, 1.0 mmol), the cross-linker 3
(0.42 mmol), styrene (0.80 mL, 7.0 mmol), and AIBN (41 mg,
0.28 mmol, 3 mol%) was stirred in THF (21.6 mL) at 70 °C for 4 days
under nitrogen. After allowing the reaction to come to room
Et3N, CH2Cl2
+
SO2Cl
DMAP
O
H2N
NH2
H2N
HN
S
O
1
2
y
O
S
AIBN
THF
x
+
+
2
or
NH
NH2
H2
C
O
O
O
n
z
n=2,4,6
R
3
4
4a: R=
4b: R=
CH2O(CH2)2OCH2
CH2O(CH2)4OCH2
4c: R=
4d: R=
CH2O(CH2)6OCH2
Scheme 1.

380
J. Deng et al. / Reactive & Functional Polymers 72 (2012) 378–382
temperature, the reaction mixture was concentrated in vacuo to
about 5 mL, and slowly added to cold (0 °C) vigorously stirred EtOH
(100 mL). The precipitated polymer was filtered, washed with cold
EtOH, and dried in vacuo to give microgel-supported chiral TsDPEN
4 as a colorless finely divided powder in a 73–82% yield.
2.5.5. Asymmetric hydrogenation of 2-chloroacetophenone
The enantiomeric excess of (S)-1(2-chlorophenyl)-1-ethanol
was determined by chiral HPLC: column, Chiralcel OD; eluent,
1:20 2-propanol–hexane; temperature 30 °C; flow rate, 0.2 mL/
min; tR (R) = 30.8 min, tR (S) = 32.0 min.
4a: IR (NaCl)
150 MHz) d: 39.35, 124.60, 126.64, 126.72, 126.94, 144.06. Anal.
Calcd. for (C8H8)0.83(C22H22N2SO2)0.12(C10H10 0.05 C, 84.89; H,
7.12; N, 2.43. Found: C, 84.94; H, 7.03; N, 2.41.
4b: IR (NaCl)
: 3302, 3260, 1329 cmÀ1 13C NMR (CDCl3,
150 MHz) d: 39.44, 73.93, 124.47, 124.62, 124.67, 124.76, 144.14.
t
: 3313, 3271, 1330 cmÀ1; 13C NMR (CDCl3,
2.5.6. Asymmetric hydrogenation of 4-nitroacetophenone
The enantiomeric excess of (S)-1-(4-nitrophenyl)-1-ethanol was
determined by chiral HPLC: column, Chiralcel OD; eluent, 1:99
2-propanol–hexane; temperature 30 °C; flow rate, 0.4 mL/min; tR
(R) = 48.3 min, tR (S) = 52.4 min.
)
:
t
;
Anal. Calcd. for (C8H8)0.83(C22H22N2SO2)0.12(C20H22O2)0.05
84.23; H, 7.14; N, 2.29. Found: C, 84.29; H, 7.10; N, 2.22.
4c: IR (NaCl)
150 MHz) d: 25.54, 40.54, 70.12, 124.71, 126.65, 127.02, 127.31,
:
C,
3. Results and discussion
t ;
: 3300, 3264, 1329 cmÀ1 13C NMR (CDCl3,
3.1. Synthesis of microgel-supported chiral TsDPEN
144.41. Anal. Calcd. for (C8H8)0.83(C22H22N2SO2)0.12(C22H26O2)0.05
:
C, 84.25; H, 7.21; N, 2.27. Found: C, 84.16; H, 7.17; N, 2.17.
4d: IR (NaCl)
150 MHz) d: 25.48, 29.68, 40.30, 70.34, 125.60, 127.89, 128.03,
145.11. Anal. Calcd. for (C8H8)0.83(C22H22N2SO2)0.12(C24H30O2)0.05
C, 84.26; H, 7.27; N, 2.25. Found: C, 84.09; H, 7.13; N, 2.15.
Microgel-supported chiral TsDPEN 4 was synthesized as shown
in Scheme 1. The starting material, (S,S)-1,2-diphenylethylenedi-
amine 1, was treated with p-vinylbenzene sulfonyl chloride in the
presence of triethylamine to give the monomeric analog 2 in 85%
yield [27]. Subsequently, compound 2 was copolymerized with sty-
rene and one of four different cross-linkers 3 under polymerization
conditions reported for microgels [21–23] to prepare four distinct
microgel-supported chiral TsDPEN-containing polymers 4a–d. Final
yields of these polymers ranged from 73% to 82%. The chiral TsDPEN
content (loading) was determined by the nitrogen analysis of
the polymer and was in fair agreement with the theoretical value.
The number average molecular weight (Mn) and molecular weight
distribution (Mw/Mn) of polymers 4a–d were determined by GPC
relative to polystyrene standards (Table 1). The thermal stability
of polymers 4a–d was investigated by thermogravimetric analysis
to demonstrate that these polymers are stable at temperatures up
to ca. 250 °C (Table 1). The good thermal stability of these polymers
indicates that they are appropriate for use in many organic transfor-
mations at room temperature or at elevated temperatures.
t ;
: 3311, 3261, 1332 cmÀ1 13C NMR (CDCl3,
:
2.5. Asymmetric hydrogenation of aromatic ketones with
homogeneous polymeric catalysts prepared from microgel-supported
chiral TsDPEN
A 50 mL round-bottomed flask equipped with a magnetic stir bar
and a reflux condenser was charged with microgel-supported chiral
TsDPEN 4 (0.05 mmol), [RuCl2(cymene)]2 (15 mg, 0.025 mmol) and
dry DMF (5 mL). The above mixture was degassed and stirred at
80 °C for 2 h under nitrogen. After evaporating the reaction mixture
to dryness under reduced pressure the aromatic ketone (5.0 mmol)
and an azeotrope of formic acid and triethylamine (5:2) (5 mL) were
added in turn. The mixture was stirred at 35 °C and monitored by
TLC. After the reaction was complete, the clear brown solution
was concentrated to about 5 mL and poured into cold (0 °C) vigor-
ously stirred EtOH (50 mL). The precipitated polymer was filtered
and washed with cold EtOH. The filtrate was concentrated in vacuo
and the conversion was determined by GC analysis.
Furthermore, microgel-supported chiral TsDPEN 4a–d were sol-
uble in DCM, THF, DMF and toluene, but these polymers were
found to be insoluble in MeOH and EtOH. Thus, these microgels
can be readily isolated by precipitation from MeOH or EtOH.
3.2. Asymmetric hydrogenation of aromatic ketones with microgel-
supported chiral Ru–TsDPEN
2.5.1. Asymmetric hydrogenation of acetophenone
The enantiomeric excess of (S)-1-phenylethanol was deter-
mined by chiral HPLC: column, Chiralcel OD; eluent, 1:20 2-propa-
nol–hexane; temperature 30 °C; flow rate, 0.4 mL/min; tR
(R) = 18.5 min, tR (S) = 20.9 min.
One of the most important asymmetric reactions developed
that uses enantiopure TsDPEN as a chiral ligand is the hydrogena-
tion of ketones developed by Noyori et al. [5]. To demonstrate the
efficiency of the microgel-supported chiral TsDPEN strategy, we
performed asymmetric hydrogenation reactions using acetophe-
none as a model substrate. The microgel-supported chiral TsDPEN
4a–d were treated at 80 °C with [RuCl2(cymene)]2 in DMF to form
2.5.2. Asymmetric hydrogenation of propiophenone
The enantiomeric excess of (S)-1-phenyl-1-propanol was deter-
mined by chiral HPLC: column, Chiralcel OD; eluent, 1:99 2-propa-
nol–hexane; temperature 30 °C; flow rate, 0.5 mL/min; tR
(R) = 25.1 min, tR (S) = 27.1 min.
Table 1
Characterization of polymers 4a–d.
Polymer Yielda (%) Loadingb
(mmol/g)
Mnc
Mwc
Mn/
Tdd (°C)
2.5.3. Asymmetric hydrogenation of 4-methoxyacetophenone
The enantiomeric excess of (S)-1-(4-methoxyphenyl)-1-ethanol
was determined by chiral HPLC: column, Chiralcel OD; eluent, 1:20
2-propanol–hexane; temperature 30 °C; flow rate, 0.2 mL/min; tR
(R) = 40.7 min, tR (S) = 45.0 min.
Mwc
Theor. Obsd.
4a
4b
4c
4d
79
81
82
73
1.73
1.63
1.62
1.60
1.72
1.58
1.58
1.53
6500 13,600 2.1
7300 13,100 1.8
7500 11,200 1.5
7900 17,300 2.2
250
275
388
398
a
b
c
2.5.4. Asymmetric hydrogenation of 4-methylacetophenone
The enantiomeric excess of (S)-1-(4-methylphenyl)-1-ethanol
was determined by chiral HPLC: column, Chiralcel OD; eluent,
1:99 2-propanol–hexane; temperature 30 °C; flow rate, 0.5 mL/
min; tR (R) = 60.3 min, tR (S) = 62.5 min.
After purification by precipitation in EtOH.
Loading was calculated by the nitrogen analysis of polymers.
As determined by GPC relative to polystyrene standards.
d
Td is the onset decomposition temperature, evaluated as 5% weight loss and
was determined by TGA at a heating rate of 10 °C/min in nitrogen.

J. Deng et al. / Reactive & Functional Polymers 72 (2012) 378–382
381
the corresponding microgel-supported Ru complexes. The poly-
meric Ru complexes obtained were then used in the asymmetric
hydrogenation of acetophenone along with the azeotrope of formic
acid and triethylamine (5:2) as the hydrogen donor. Common fac-
tors governing the enantioselectivity and conversion of the reac-
tion were examined. The results are shown in Table 2.
We found that acetophenone was smoothly hydrogenated to
give (S)-1-phenylethanol (the absolute configuration of the prod-
uct was determined by comparison with a standard obtained using
Noyori’s ligand [5]) in 74–100% conversion with ligands 4a–d, and
the corresponding enantiomeric excesses were 92–96% (Entries
1–4). These data show that the different of polymer’s inner struc-
ture had some effect on reaction conversion but had little impact
on enantioselectivity. The best result was obtained with ligand
4c (Entry 3).
The solvent used in a reaction is often important, so we investi-
gated the asymmetric hydrogenation of acetophenone with ligand
4c in different solvents, including DCM, DMF, THF and toluene
(Entries 3, 5–7). A noticeable decrease in conversion was observed
when using DMF, THF or toluene as the solvent with ligand 4c.
Thus, DCM was determined to be the best solvent for this hydroge-
nation reaction with ligand 4c.
The effect of temperature on the asymmetric hydrogenation of
acetophenone using ligand 4c in DCM was also investigated. When
the reaction was carried out at 0 °C or 20 °C (Entries 8, 9), low con-
versions were obtained. Thus, the temperature of 35 °C is more
suitable for this reaction.
both a NCPS-supported catalyst and a PS-supported catalyst under
our optimal conditions (Entries 13, 14). In these experiments, the
level of enantioselectivity generated by the NCPS-supported cata-
lyst and the PS-supported catalyst was similar to the microgel-sup-
ported catalyst, but higher conversion was obtained using the
microgel-supported catalyst. This result may be ascribed to the
advantages of microgels (e.g., high solubility and low viscosity).
Isolation of the product by simple recrystallization and filtra-
tion was quite easy when using the microgel-supported chiral
catalyst. Catalyst recycling experiments could also be readily per-
formed. After the hydrogenation reaction was complete, the micro-
gel-supported catalyst could be collected by precipitation and
filtration and was ready for use in another reaction. We have per-
formed the asymmetric hydrogenation of acetophenone four times
with the same microgel-supported chiral TsDPEN 4c-dervived cat-
alyst (Entries 3, 15–17). This experiment clearly shows that there is
no decrease in conversion or enantioselectivity caused by recycling
the catalyst. Metal leaching was studied by performing an ICP-AES
analysis of the catalyst before and after each reaction in the cata-
lyst recycling experiment. As is shown in Table 3, the ruthenium
concentration in the microgel supported catalyst decreased
slightly in every cycle, which confirmed that a negligible amount
of ruthenium leaching was occurring with each cycle.
In addition to acetophenone, various other aromatic ketones
were also subjected to asymmetric hydrogenation with the homo-
geneous polymeric catalyst derived from microgel-supported chi-
ral TsDPEN 4c. Quantitative conversion was attained for all of the
ketones hydrogenated in Table 4. The corresponding secondary
alcohols were obtained in high enantiomeric excess by means of
the homogeneous polymeric chiral catalyst. Asymmetric hydroge-
nation of 2-chloroacetophenone afforded 1-(2-chlorophenyl)etha-
nol in 98% ee. It is noteworthy that complete conversion was
observed in only 4 h when using 2-chloroacetophenone or 4-nitro-
acetophenone as the substrate. These results show that the
homogeneous polymeric chiral catalyst system prepared from 4c
is highly active in asymmetric hydrogenation reactions of aromatic
Furthermore, the molar ratio of substrate to catalyst (S/C) was
investigated (Entries 3, 10–12). The hydrogenation of acetophe-
none using 4c at an S/C ratio of 100 provided the best results with
96% ee at 100% conversion (Entry 3), while the highest S/C ratio of
1000 led to a lower reaction rate and decreased enantioselectivity
(Entry 12).
To compare the catalytic activity of the microgel-supported cat-
alyst with immobilized catalysts of similar molecular weight, we
performed the asymmetric hydrogenation of acetophenone with
Table 2
Asymmetric hydrogenation of acetophenone using microgel-supported chiral catalyst.a
OH
O
4, [RuCl2(cymene)]2
Et3N/HCOOH
Entry
Ligand
S/C
Solvent
Temp (°C)
Time (h)
Convb (%)
Eec (%)
Config
1
2
3
4
5
6
7
8
4a
4b
4c
4d
4c
4c
4c
4c
4c
4c
4c
4c
100
100
100
100
100
100
100
100
100
200
500
1000
100
100
100
100
100
DCM
DCM
DCM
DCM
DMF
THF
Toluene
DCM
DCM
DCM
DCM
DCM
DCM
DCM
DCM
DCM
DCM
35
35
35
35
35
35
35
0
20
35
35
35
35
35
35
35
35
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
74
83
100
78
31
43
46
2
53
63
31
11
80
45
97
92
88
93
92
96
92
89
91
93
–
96
85
93
76
96
94
95
92
90
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
9
10
11
12
13d
14e
15
16
17
NCPS-supported TsDPEN
PS-supported TsDPEN
4c (second)
4c (third)
4c (fourth)
a
Reactions were conducted using acetophenone (5 mmol), solvent (5 mL), Et3N/HCOOH mixture (5 mL), microgel-supported chiral TsDPEN 4 (0.05 mmol) and [RuCl2(-
cymene)]2 (15 mg, 0.025 mmol).
b
Determined by GC.
Determined by HPLC using chiralcel OD.
c
d
NCPS-supported TsDPEN was prepared by copolymerization of the chiral monomer 2 with styrene in the same monomer radio as microgel-supported TsDPEN.
PS-supported TsDPEN was prepared by copolymerization of the chiral monomer 2 with styrene and a frequently-used cross-linker divinylbenzene in the same monomer
e
radio as microgel-supported TsDPEN.

382
J. Deng et al. / Reactive & Functional Polymers 72 (2012) 378–382
Table 3
noteworthy that in all cases, the performance of the soluble
polymeric microgels was shown to be equivalent to or better than
comparable insoluble cross-linked polymers-based catalysts. Addi-
tionally, these polymer catalysts do not necessitate the use of any
special equipment to monitor progress of reactions, which makes
them attractive from a cost standpoint.
Ru concentration of microgel-supported catalyst in the recycling
experiments.
Cycle
Ru concentration (%)
1
2
3
4
7.95
7.86
7.73
7.58
Acknowledgments
We gratefully acknowledge the National Natural Sciences Foun-
dation of China (No. 21042005), the Natural Sciences Foundation of
Hubei Province in China (No. 2010CDA019) and the 2011 National
Major Scientific Instrument and Equipment Development Project
(No. 2011YQ12003505) for financial support.
Table 4
Asymmetric hydrogenation of aromatic ketones using microgel-supported chiral
catalyst.a
OH
O
4c, [RuCl2(cymene)]2
Et3N/HCOOH
Ar
Entry Aromatic ketone
Ar
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4. Conclusions
In conclusion, we have prepared four distinct microgel-sup-
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pure chiral TsDPEN monomer with styrene and one of four
cross-linkers. Asymmetric hydrogenations of aromatic ketones
performed with the complex generated from the homogeneous
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