New chiral cationic rhodium-aminophosphine complexes for asymmetric transfer hydrogenation of aromatic ketones

Article abstract of DOI:10.1016/S0022-328X(99)00565-3

The new chiral ligands (S,S)-N,N′-bis[o-(diphenylphosphino)benzylidene]1,2-diiminocyclohexane, [(S,S)-1] and (S,S)-N,N′-bis[o-diphenylphosphino]benzyl-1,2-diaminocyclohexane, [(S,S)-2] have been prepared. The interaction of [(S,S)-1] and [(S,S)-2] with [Rh(COD)Cl]₂ afforded the corresponding cationic rhodium complexes [(S,S)-3][X] and [(S,S)-4][X] (X=PF₆^-, BF₄^- or ClO₄^-), respectively. [(S,S)-1], [(S,S)-2], [(S,S)-3][X] and [(S,S)-4][X] have been fully characterized by elemental analyses and spectroscopic methods. These chiral cationic rhodium complexes serve as catalytst precursors for the asymmetric transfer hydrogenation of acetophenone derivatives in 2-propanol and [(S,S)-4][PF₆] acts as an excellent catalyst in the reduction of m-chloroacetophenone, giving the corresponding optical alcohols in 99% yield and up to 94% ee.

Full text of DOI:10.1016/S0022-328X(99)00565-3

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 592 (1999) 290–295
New chiral cationic rhodium–aminophosphine complexes for
asymmetric transfer hydrogenation of aromatic ketones
a,
a
a
a
a
Jing-Xing Gao *, Xiao-Dong Yi , Pian-Pian Xu , Chun-Liang Tang , Hui-Lin Wan ,
b
Takao Ikariya
a
Department of Chemistry, Institute of Physical Chemistry, State Key Laboratory for Physical Chemistry of Solid Surfaces, Xiamen Uni6ersity,
Xiamen 361005 Fujian, PR China
Department of Chemical Engineering, Faculty of Engineering, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku,
b
Tokyo 152-8552, Japan
Received 1 June 1999; accepted 22 September 1999
Abstract
The new chiral ligands (S,S)-N,N%-bis[o-(diphenylphosphino)benzylidene]1,2-diiminocyclohexane, [(S,S)-1] and (S,S)-N,N%-
bis[o-diphenylphosphino]benzyl-1,2-diaminocyclohexane, [(S,S)-2] have been prepared. The interaction of [(S,S)-1] and [(S,S)-2]
−
6
−
4
with [Rh(COD)Cl]2 afforded the corresponding cationic rhodium complexes [(S,S)-3][X] and [(S,S)-4][X] (X=PF , BF or
−
4
ClO ), respectively. [(S,S)-1], [(S,S)-2], [(S,S)-3][X] and [(S,S)-4][X] have been fully characterized by elemental analyses and
spectroscopic methods. These chiral cationic rhodium complexes serve as catalytst precursors for the asymmetric transfer
hydrogenation of acetophenone derivatives in 2-propanol and [(S,S)-4][PF ] acts as an excellent catalyst in the reduction of
6
m-chloroacetophenone, giving the corresponding optical alcohols in 99% yield and up to 94% ee. © 1999 Elsevier Science S.A. All
rights reserved.
Keywords: Chiral ligand; Chiral rhodium complexes; Transfer hydrogenation; Prochiral ketone; Asymmetric reduction
1. Introduction
‘hard’ nitrogen atoms as chelating reagents for prepara-
tion of mono- and bi-metallic center complexes [20–23].
The bidentate and polydentate phosphines are impor-
We previously reported that trans-RuCl complex with
2
tant ligands in coordination chemistry and homoge-
neous catalysis. Optically active phosphine ligands,
such as DIOP, CHIRAPHOS and BINAP, play a
crucial role in asymmetric catalysis [1]. Recently, opti-
cally active nitrogen compounds were proved to be
efficient ligands in enantioselective catalysis [2–4] and
some chiral Ir, Rh and Ru complexes bearing nitrogen
donor atoms have been developed with great successes
for asymmetric transfer hydrogenation [5–12]. The im-
portance and application of chiral phosphine ligands
and nitrogen ligands have been further extented by
combining phosphorus centers and nitrogen donor
atoms in PN [13], NPN [14], PNP [15,16] or PNNP type
ligands [17–19]. In the past few years, we have been
interested in the synthesis of well-designed PNNP type
ligands possessing two ‘soft’ phosphorus atoms and two
a chiral tetradentate aminophosphine ligand is an excel-
lent catalyst precursor for asymmetric transfer reduc-
tion of aromatic ketone [24]. As an extension of the
ongoing research program, we would like to describe
the synthesis and characterization of some new cationic
rhodium–aminophosphine complexes and their appli-
cation in the asymmetric hydrogen transfer reduction of
aromatic ketones in this paper.
2. Experimental
2.1. General
All experiments were carried out in a nitrogen atom-
sphere with Schlenk and syringe techniques. All sol-
vents were dried and purified according to standard
methods before use. IR spectra were recorded on a
*
Corresponding author.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00565-3

J.-X. Gao et al. / Journal of Organometallic Chemistry 592 (1999) 290–295
291
PE-Spectroy 2000 spectrophotometer. NMR spectra
2.4. Synthesis of [Rh(S,S)-cycloC P N ][PF ],
6 2 2 6
were recorded on a Varian Unity-500 spectrometer.
[(S,S)-3][PF6]
1
H-NMR chemical shifts are reported in ppm relative
3
1
to TMS. P spectra were referenced to 85% H PO
To a mixture of ligand [(S,S)-1] (0.20 g, 0.30 mmol)
3
4
as an external standard. The element analyses were
carried out on a Fisons EA 1110. All melting points
were measured in sealed tubes and were not
corrected.
and [Rh(COD)Cl] (0.074 g, 0.15 mmol) were added
2
benzene (6 ml) and methanol (6 ml). The mixture was
stirred at room temperature for 12 h. After removal of
solvent, the residue was dissolved in a minimum of
methanol and precipitated by addition of a solution of
NH PF6 (0.082 g, 0.5 mmol) in H O (3 ml). The
4
2
2
.2. Synthesis of (S,S)-cycloC P N , [(S,S)-1]
precipitate was collected and washed successively with
6
2
2
H O (3 ml×3) and diethyl ether (3 ml), then dried in
2
A mixture of (S,S)-1,2-diaminocyclohexane (0.35 g,
.0 mmol), o-(diphenylphosphino)benzaldehyde (1.74 g,
.0 mmol) and anhydrous Na SO (2.56 g, 18.0 mmol)
vacuo to afford [(S,S)-3][PF ] as a yellow solid (0.20 g,
6
3
6
74% yield). m.p. 245°C (dec.). IR (KBr pellet, w
−
1
(cm )): 3414 m, 3055 m, 2931 m, 2857 w, 1630 m,
1555 w, 1435 s, 1177 m, 1099 s, 750 m, 696 vs, 570 w,
2
4
in CH Cl (20 ml) was stirred for 24 h. A pale-orange
2
2
1
solution was obtained. The solution was filtered, and
then concentrated under reduced pressure to ca. 5 ml.
To the solution was added 20 ml of ethanol and the
resulting solution was cooled to −20°C to give a
yellow solid, filtered and dried in vacuo (1.78 g, 90%
536 vs. H-NMR (CDCl ): l 1.24 (m, 2H, CH ), 1.36
3
2
(m, 2H, J=13.5 Hz, CH ), 1.46 (m, 2H, CH ),1.66 (d,
2
2
2H, J=8.0 Hz, CH ), 3.12 (m, 2H, CH), 6.80–7.75 (m,
2
3
1
28H, Ar), 8.69 (d, 2H, J=4.0 Hz, ArCHꢀN). P-
NMR: l 39.60. Anal. Found: C, 56.85; H, 4.85; N,
2.87. C H N F P Rh·H O. Calc.: C, 57.15; H, 4.59;
−
1
yield). m.p. 60ꢀ62°C. IR (KBr pellet, w (cm )): 3049
44
40
2
6
3
2
m, 2928 s, 2857 s, 1636 s, 1433 s, 1087 w, 748 vs, 697 vs,
N, 3.03%.
1
5
47 w, 503 s. H-NMR (CDCl ): l 1.26 (m, 2H, CH ),
3
2
1
.38 (d, 2H, J=7.8 Hz, CH ), 1.45 (m, 2H, CH ), 1.65
2.5. Synthesis of [Rh(S,S)-cycloC P N H ][PF ],
2
2
6
2
2
4
6
(
d, 2H, J=6.0 Hz, CH ), 3.11 (m, 2H, CH), 6.79–7.74
[(S,S)-4][PF6]
2
(
m, 28H, Ar), 8.69 (d, 2H, J=4.0 Hz, Ar–CHꢀN).
3
1
P-NMR (CDCl ): l −12.98. Anal. Found: C, 79.10;
In a similar fashion as described for [(S,S)-3][PF6],
using ligand [(S,S)-2] instead of [(S,S)-1], [(S,S)-4][PF6]
as a yellow solid was obtained (0.19 g, 70% yield). m.p.
3
H, 6.39; N, 4.23. C H N P ·0.5C H OH. Calc.: C,
4
4
40
2
2
2
5
79.30; H, 6.31; N, 4.11%.
−
1
2
38°C (dec.). IR (KBr pellet, w (cm )): 3414 m, 3056
m, 2857 w, 1591 w, 1482 w, 1436 s, 1167 m, 1098 s, 750
1
2
.3. Synthesis of (S,S)-cycloC P N H , [(S,S)-2]
m, 723 m, 697 vs, 541 vs, 464 w. H-NMR (CDCl ): l
6
2
2
4
3
1
.21 (m, 4H, CH ), 1.77 (d, 2H, J=28.5 Hz, CH ), 2.17
2
2
A solution of compound (S,S)-1 (1.65 g, 2.5 mmol)
(br, 2H, NH), 3.19 (s, 2H, CH ), 4.01 (d, 2H, J=10
2
and NaBH (0.57 g, 15 mmol) in absolute ethanol (30
ml) was refluxed with stirring for 24 h. The solution
Hz, CH), 4.36 (m, 2H, ArCH ), 4.86 (m, 2H, ArCH ),
4
2
2
31
6.52–7.82 (m, 28H, Ar). P-NMR (CDCl ): l 33.03.
3
was cooled to room temperature and H O (10 ml) was
Anal. Found: C, 55.83; H, 5.11; N, 2.96.
C H N F P Rh·2H O. Calc.: C, 55.84; H, 5.28; N,
2
added to destroy excess NaBH . The mixture solution
4
44 44
2
6
3
2
was extracted with CH Cl (30 ml×3). The combined
2.91%.
2
2
extract was washed with 10% aqueous NH Cl (10 ml×
4
2
), H O (10 ml×2) and the organic layer was dried
2.6. Synthesis of [Rh(S,S)-cycloC P N H ]BF ,
6 2 2 4 4
2
over anhydrous Na SO filtered and concentrated to
[(S,S)-4][BF4]
2
4,
ca. 5 ml. Then 15 ml of ethanol was added and cooled
to −20°C to give cream-white crystals (1.34 g, 80%
yield). m.p. 54ꢀ56°C. IR (KBr pellet, w (cm )): 3051
In an analogous manner and using NaBF instead of
4
−
1
NH PF , [(S,S)-4][BF ] as a yellow solid was isolated
4
4
4
m, 2924 s, 2852 m, 1565 w, 1433 s, 1183 m, 1114 m, 746
(0.20 g, 77% yield). m.p. 194°C (dec.). IR (KBr pellet, w
(cm )): 3405 m, 3232 m, 2932 m, 2862 w, 1589 w,
1
−1
vs, 696 vs, 544m, 502 m. H-NMR (CDCl ): l 0.87 (m,
3
2
H, CH ),1.08 (t, 2H, CH ), 1.58 (d, 2H, J=6.4 Hz,
1436 s, 1170 m, 1095 vs, 751 m, 697 s, 539 s, 466 w.
2
2
1
CH ), 1.87 (br, 2H, NH-), 1.98 (d, 2H, J=12.8 Hz,
H-NMR (CDCl ): l 0.87 (m, 2H, CH ), 1.08 (m, 2H,
2
3
2
CH ), 2.11 (d, 2H, J=8.5 Hz, CH), 3.82 (d, 2H,
CH ), 1.59 (d, 2H, J=7.5 Hz, CH ), 1.98 (m, 4H,
2
2
2
J=13.6 Hz, ArCH ), 4.00 (d, 2H, J=13.6 Hz,
CH ), 2.13 (m, 2H, NH), 3.83 (d, 2H, J=13.5 Hz,
2
2
3
1
ArCH –), 6.81–7.52 (m, 28H, Ar). P-NMR: l −
ArCH ), 4.00 (d, 2H, J=13.5 Hz, ArCH ), 6.82–7.52
2
2
2
31
15.21. Anal. Found: C, 78.39; H, 6.78; N, 4.27.
(m, 28H, ArCH2). P-NMR (CDCl ): l 32.56. Anal.
3
C H N P ·0.5C H OH. Calc.: C, 78.83; H, 6.86; N,
Found: C, 59.33; H, 5.74; N, 3.04. C H N BF P Rh.
4
4
44
2
2
2
5
44 44
2
4 2
4.23%.
Calc.: C, 59.47; H, 5.46; N, 3.15%.

292
J.-X. Gao et al. / Journal of Organometallic Chemistry 592 (1999) 290–295
2
.7. Synthesis of [Rh(R,R)-cycloC P N H ][ClO ],
diphosphino)benzyl]cyclohexane-1,2-diamine (S,S)-2 in
75–81% yield. In the H-NMR spectrum the presence
6
2
2
4
4
1
[(R,R)-4][ClO4]
of (S,S)-2 at l 1.87 for the –NH– protons and the
−
1
[
(R,R)-4][ClO ] was prepared by means of the above
disappearance of infrared band at 1636 cm
indicate
4
similar procedures. The product was contaminated
that the two imino groups were reduced to the corre-
31
somewhat with NaClO and was further purified by
sponding diamino groups. The
P-NMR spectra
4
washing with H O and extracting with CH Cl . The
solvent was removed in vacuo. The resulting residue
present a singlet at l −15.21 in accord with two
equivalent phosphino groups.
2
2
2
was recrystallized from CH Cl /hexane to afford an
In an analogous procedure the ligands (R,R)-1 or
(R,R)-2 were also prepared.
2
2
analytical sample (0.18 g, 70% yield). m.p. 116°C (dec.).
−
1
IR (KBr pellet, w (cm )): 4324 m, 3056 m, 2933 m,
2
6
858 w, 1590 w, 1436 m, 1159 m, 1094 vs, 751m, 697 s,
3
.2. Synthesis and characterization of cationic
1
29 w, 524 s, 467 w. H-NMR (CDCl ): l 0.89 (m, 2H,
3
rhodium–aminophosphine complexes
CH ), 1.10 (m, 2H, CH ), 1.60 (d, 2H, J=8.5 Hz,
2
2
CH ), 2.02 (m, 2H, NH), 2.15 (d, 2H, J=8.5 Hz, CH),
2
Treatment of [Rh(COD)Cl] with (S,S)-cycloC P N
2
(S,S)-1] in an 1:1 mixture of methanol–benzene and
then precipitation by the addition of a solution of
2
6
2
3
4
.83 (d, 2H, J=13.5 Hz, CH ), 3.89(m, 2H, ArCH ),
2
2
[
31
.00 (m, 2H, ArCH ), 6.82–7.62 (m, 28H, Ar). P-
2
NMR (CDCl ): l 32.81. Anal. Found: C, 63.66; H,
3
NH PF in water afforded a yellow solid of cationic
4
6
5
6
.72; N, 2.75. C H N O ClP Rh·C H Calc.: C,
3.12; H, 6.16; N, 2.95%.
44 44 2 4 2 6 14
31
rhodium complex (S,S)-3 in 74% yield. The P-NMR
spectrum of (S,S)-3 exhibited a singlet at 39.60 indicat-
ing that the two phosphino groups of the (S,S)-1 ligand
were coordinated and equivalent (Scheme 2). Com-
plexes [(S,S)-4][PF ], [(S,S)-4][BF ] and [(S,S)-4][ClO ]
2.8. Typical procedure for asymmetric transfer
hydrogenation of ketones
6
4
4
were also prepared by a similar procedure and by the
The catalyst precursor (0.01 mmol) was added to a
Schlenk tube and 2-propanol (20 ml), iso-PrOK/iso-
PrOH solution (0.1 M, 0.1 ml) were introduced under
nitrogen. The mixture was stirred for 10 min, acetophe-
none was added and the solution was stirred for the
required reaction time. At the end of the experiment,
the reaction products were analyzed by capillary gas
chromatography.
addition of a solution of NH PF , NaBF or NaClO ,
4
4
4
4
respectively (Scheme 1). While using (R,R)-1 or (R,R)-2
instead of (S,S)-1, the corresponding complexes (R,R)-
3
and (R,R)-4 were also isolated. All these complexes
have been fully characterized by elemental analyses and
IR and NMR spectroscopic methods.
3.3. Asymmetric transfer hydrogenation of aromatic
ketones with cationic rhodium(I) complexes as catalysts
3. Results and discussion
In the studies of asymmetric transfer hydrogenation
of aromatic ketones, the 2-propanol/potassium 2-pro-
poxide system has been used as a source of hydrogen.
New cationic rhodium(I) complexes as catalyst precur-
sors for the reduction of acetophenone have been exam-
ined (Scheme 2) and typical results are summarized in
Table 1.
A mixture system from [Rh(COD)Cl]2 and ligand
(R,R)-2 as catalyst precursor only gave low conversion
and enantioselectivity (Table 1, Run 1). When cationic
rhodium(I) complex with diiminodiphosphine ligand
(R,R)-3 was used, the activity and ee were still low
(Table 1, Run 2). However, when cationic rhodium(I)
complexes containing diaminodiphosphine ligands were
employed as catalysts, high conversion and ee were
obtained (Table 1, Runs 3–11). These results are simi-
lar to that of earlier studies [24–26], indicating that the
NH functions in the ligands are responsible for the high
activity and the NH linkage possibly can stabilize a
catalytic transition state [11,27]. The cationic rhodi-
3
.1. Synthesis and characterization of (S,S)-1 and
(S,S)-2
(
S,S)-1 was prepared by Schiff base condensation of
o-(diphenyl-diphosphino)benzylaldehyde (2 equiva-
lents) and (S,S)-1,2-diamino-cyclohexane in di-
cholomethane with anhydrous Na SO as dehydrating
agent. A pale-yellow solid (S,S)-N,N%-bis[o-(diphenyl-
phosphino)benzylidene]-cyclohexane-1,2-diamine[(S,S)-
2
4
1
] was obtained in 87–90% yield (Scheme 1). The IR
spectrum of (S,S)-1 exhibits a strong CꢀN stretch at
1
−
1
1
636 cm . The H-NMR spectrum exhibits a doublet
(
J=4.5 Hz) at l 8.69 for the imino protons. The
3
1
P-NMR spectrum presents a singlet at l −12.98.
These spectroscopic data and results of elemental anal-
ysis indicate that (S,S)-1 contains diimino and the two
diphosphino groups are equivalent.
Reduction of the diiminodiphosphine (S,S)-1 with
excess NaBH was carried out in refluxing ethanol to
4
afford the corresponding (S,S)-N,N%-bis[o-(diphenyl-
um(I) complex [(S,S)-4][PF ] has been proved to be a
6

J.-X. Gao et al. / Journal of Organometallic Chemistry 592 (1999) 290–295
293
Scheme 1.
and ee, but [(S,S)-4][BF ] exhibited very high reactivity
4
with some loss of the enantiometric purity of the
product. The addition of ligand (R,R)-2 decreased the
reaction rate, but the highest enantioselectivity (96%)
was obtained (Table 1, Runs 8 and 11).
With the cationic rhodium(I) complex [(R,R)-4][PF6],
a variety of alkyl arylketones were transformed to the
corresponding secondary alcohols (Table 2). The reac-
tivity and enantioselectivity were very dependent on the
position of the ring substituent and the bulkiness of the
alkyl group. The introduction of both an electron-with-
drawing group such as chloro and an electron-releasing
group such as methoxyl to the meta position acceler-
ated the reaction with a high enantioselectivity (Table
2, Runs 3 and 5), while the chloro or methoxyl group to
the para position tended to lower the rate and the
stereoselectivity (Table 2, Runs 4 and 6). The reaction
rate was remarkably decreased by increasing the bulki-
ness of the alkyl group (Table 2, Runs 7–9), but the
enantioselectivity was not significantly influenced.
Scheme 2.
good catalyst, giving (R)-1-phenylethanol in 97% yield
and 91% ee after reaction for 7 h at 82°C (Table 1, Run
). Although the yields gradually decreased on increas-
3
ing the mole ratios of [acetophenone]/[Rh] from 100:1
to 400:1, the enantioselectivity was still high (Table 1,
Runs 3–6). Comparing the cationic rhodium(I) com-
−
6
−
−
plexes with various anions PF , BF and ClO4 (Table
4
1
, Runs 4, 9 and 10), [(S,S)-4][PF ] gave better yield
6

294
J.-X. Gao et al. / Journal of Organometallic Chemistry 592 (1999) 290–295
Table 1
Asymmetric transfer hydrogenation of acetophenone (7a) catalyzed by chiral Rh(I) complexes
a
Run
Catalyst precursor
Time (h)
Alcohol
Yield (%) b
ee (%) c
Configuration d
h
1
2
[Rh(COD)Cl] /(R,R)-2
[(R,R)-3][PF6]
9
7
56
40
36
40
S
S
2
3
4
5
6
7
8
9
[(S,S)-4][PF6]
[(S,S)-4][PF6]
[(S,S)-4][PF6]
[(S,S)-4][PF6]
7
12
16
24
9
24
7
9
97
86
81
85
86
58
98
87
73
91
86
89
89
89
96
80
86
92
R
R
R
R
S
S
R
S
e
f
g
[(R,R)-4][PF6]
h
[(R,R)-4][PF ]/(R,R)-2
6
[(S,S)-4][BF4]
[(R,R)-4][ClO4]
[(R,R)-4][ClO ]/(R,R)-2
1
1
0
1
h
24
S
4
a
The reaction was carried out at refluxing temperature (82°C) using catalyst (0.01 mmol), 2-propanol (20 ml) and iso-PrOK/iso-PrOH solution
(
0.1 M, 0.1 ml). [Acetophenone]:[Rh(I)]:[iso-PrOK]=100:1:1 in mole ratio, unless otherwise stated.
b
Yield was determined by GLC.
Determined by capillary GLC analysis using a Chiral Chrompack CP-cyclodextrin-b-236-M-19 column.
Determined by comparison of the retention times of the enantiomers on the GLC traces with literature values.
c
d
e
[
acetophenone]:[Rh]=200:1 in mole ratio.
f
[
acetophenone]:[Rh]=300:1 in mole ratio.
g
h
[
[
acetophenone]:[Rh]=400:1 in mole ratio.
Rh]:[(R,R)-2]=1:1 in mole ratio.
Table 2
a
Asymmetric transfer hydrogenation of alkyl aryl ketones catalyzed by [(R,R)-4][PF6]
Run
Ketone
Time (h)
Alcohol
Yield (%) b
ee (%) c
Configuration d
1
2
3
4
5
6
7
8
9
7a
7a
9
9
86
93
99
68
97
49
91
38
13
89
89
94
73
90
71
80
78
76
S
S
S
S
S
S
S
S
S
e
m-7b
p-7b
m-7c
p-7c
7d
22
22
22
22
22
22
22
7e
7f
a
The reaction was carried out in the presence of [Rh(R,R)-cycloC P N H ][PF ] (0.01 mmol) using a 0.05 M solution of ketone (1.0 mmol) in
6
2
2
4
6
2
-propanol (20 ml) at 82°C; [ketone]:[Rh]:[iso-PrOK]=100:1:1.
b
Yield was determined by GLC analysis.
c
Determined by capillary GLC analysis using a chiral CP-cyclodextrin-b-236-M-19 column.
Determined by comparison of the retention times of the enantiomers on the GLC traces with literature values.
The reaction was carried out in 2-propanol (18 ml)+THF (2 ml).
d
e
4
. Conclusions
trasted to the low reactivity of a structurally similar
diiminodiphosphine-based complex. These results sug-
gest that the NH moiety in the ligand is responsible for
the high reactivity and enantioselectivity. To our
knowledge, these are excellent enantioselective systems
for the asymmetric transfer hydrogenation of ketone
catalyzed by chiral rhodium complexes. In order to
reveal the exact reaction mechanism, isolation and
characterization of the catalytic active species is under
further investigation.
In summary, we have synthesized the new cationic
rhodium(I) complexes with chiral diimino- or di-
aminodiphosphine tetradentate ligands and investigated
their use in asymmetric transfer hydrogenation of ke-
tone. The asymmetric catalysis attains a high efficiency
using rhodium(I) complexes with diaminodiphosphine
tetradentate ligands. The high catalytic activity is con

J.-X. Gao et al. / Journal of Organometallic Chemistry 592 (1999) 290–295
295
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Acknowledgements
[
[
10] A. Fujii, S. Hashiguchi, N. Uematsu, T. Ikariya, R. Noyori, J.
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The authors thank the National Natural Science
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