New chiral rhodium and iridium complexes with chiral diamine ligands for asymmetric transfer hydrogenation of aromatic ketones

Full text of DOI:10.1021/jo990213a

2186
J . Org. Chem. 1999, 64, 2186-2187
New Ch ir a l Rh od iu m a n d Ir id iu m Com p lexes
w ith Ch ir a l Dia m in e Liga n d s for Asym m etr ic
Tr a n sfer Hyd r ogen a tion of Ar om a tic Keton es
Kunihiko Murata and Takao Ikariya*
Department of Chemical Engineering, Faculty of Engineering,
Tokyo Institute of Technology and CREST, J apan Science and
Technology Corporation, 2-12-1 O-okayama, Meguro-ku,
Tokyo 152-8552 J apan
Ryoji Noyori
Department of Chemistry and Research Center for Materials
Science, Nagoya University, Chikusa, Nagoya 464-8602 J apan
Received February 4, 1999
Catalytic asymmetric transfer hydrogenation using 2-pro-
panol or formic acid as a hydrogen source is a useful
complement to catalytic asymmetric hydrogenation as a
practical tool for the stereoselective synthesis of chiral
alcohols or amines.1,2 We have recently developed highly
efficient chiral diamine-based Ru(II) catalysts, RuCl(Tsd-
pen)(µ6-arene) (1a ) (TsDPEN: N-(p-toluenesulfonyl)-1,2-
diphenylethylenediamine) for the asymmetric transfer hy-
drogenation of ketones and imines to chiral alcohols and
amines with excellent enantiomeric purities.3 The Ru(II)-
catalyzed hydrogen transfer reaction was found to be
promoted by an isolable 18-electron chiral Ru hydride (1b)
or 16-electron Ru amide (1c) complex, which is a catalyst or
intermediate derived from catalyst precursor 1a . The con-
version of 1b to 1c in the catalysis takes place by the action
of ketones or imines possibly via a six-membered cyclic
transition state stabilized by a hydrogen bond between an
NH moiety in the ligand and C)X (X ) O, NR).3f,i This
metal/ligand bifunctional effect, therefore, results in excel-
lent catalyst performance in terms of the rate and the
enantioselectivity for the catalytic reduction using molecular
hydrogen4 or organic hydrogen sources.5 We now disclose a
synthesis of a new type of rhodium or iridium complex,
Cp*MCl(Tsdiamine) (M ) Rh, Ir), which has a structure
isoelectronic with the chiral Ru complex (1a ).3a,f These
isolable complexes have proved to efficiently catalyze the
asymmetric hydrogen transfer of simple aromatic ketones
in 2-propanol containing a base.
The chiral Rh or Ir complexes with Cp* and chiral diamine
ligands were prepared as orange to yellow crystals (2a -4a )
by reacting [Cp*MCl2]2 with (R,R)-TsCYDN or (R,R)-TsD-
PEN ([Cp*MCl2]2/diamine/base ) 1:2:4.2, Cp*: pentameth-
ylcyclopentadienyl, M ) Rh, Ir; (R,R)-TsCYDN: (1R,2R)-N-
(p-toluenesulfonyl)-1,2-cyclohexanediamine) in the presence
of (C2H5)3N at room temperature. 1H NMR analysis of these
complexes confirms the diastereoselective formation of a
single stereoisomer.6 The single-crystal X-ray crystallo-
graphic analysis of Cp*RhCl[(R,R)-Tscydn] (2a ) illustrated
in Figure 1 shows that 2a has a distorted octahedral
coordination environment with Cp*, amino, sulfonamido,
and chloro ligands.6 The chirality of the (R,R)-diamine ligand
that forms a λ-configured five-membered ring determines the
S configuration at the central metal as observed in the chiral
Ru complex (1a ). It should be noted that there is a very short
Cl‚‚‚N distance (2a : 2.70, 3a : 2.66, 4a : 2.70 Å) that is
ascribed to intramolecular hydrogen bonding. Since Cp*MCl-
(diamine) has an acidic proton on the N atom, the facile
elimination of HCl with a base in alcohols gave an isolable
hydride complex through the amide complex. For example,
(4) Before this finding of an NH effect in the transfer hydrogenation of
ketones, the same effect had been proposed in asymmetric hydrogenations
catalyzed by the Ru-BINAP-diamine catalyst system. See: (a) Ohkuma, T.;
Ooka, H.; Hashiguchi, S.; Ikariya, T.; Noyori, R. J . Am. Chem. Soc. 1995,
117, 2675-2676. (b) Ohkuma, T.; Ooka, H.; Ikariya, T.; Noyori, R. J . Am.
Chem. Soc. 1995, 117, 10417-10418. (c) Ohkuma, T.; Yamakawa, M.;
Ikariya, T.; Noyori, R. J . Org. Chem. 1996, 61, 4872-4873. (d) Ohkuma,
T.; Ikehira, H.; Ikariya, T.; Noyori, R. Synlett 1997, 467-468. (e) Ohkuma,
T.; Doucet, H.; Pham, T.; Mikami, K.; Korenaga, T.; Terada, M.; Noyori, R.
J . Am. Chem. Soc. 1998, 120, 1086-1087. (f) Doucet, H.; Ohkuma, T.;
Murata, K.; Yokozawa, T.; Kozawa, M.; Katayama, E.; England, A. F.;
Ikariya, T.; Noyori, R. Angew. Chem., Int. Ed. Engl. 1998, 37, 1703-1707.
(5) (a) Pu¨ntener, K.; Schwink, L.; Knochel, P. Tetrahedron Lett. 1996,
37, 8165-8168. (b) J iang, Y.; J iang, Q.; Zhu, G.; Zhang, X. Tetrahedron
Lett. 1997, 38, 6565-6568. (b) Inoue, S.; Nomura, K.; Hashiguchi, S.; Noyori,
R.; Izawa, Y. Chem. Lett. 1997, 957-958. (c) Halle, R. T.; Bre´he´ret, A.;
Schulz, E.; Pinel, C.; Lemaire, M. Tetrahedron: Asymmetry 1997, 8, 2101-
2108. (d) Palmer, M.; Walsgrove, T.; Wills, M. J . Org. Chem. 1997, 62, 5226-
5228. (e) Stinson, S. C. Chem. Eng. News 1998, 76, 6 (22), 15-24. (f) Alonso,
D. A.; Guijarro, D.; Pinho, P.; Temme, O.; Anderson, P. G. J . Org. Chem.
1998, 63, 2749-2751. (g) J iang, Y.; J iang, Q.; Zhang, X. J . Am. Chem. Soc.
1998, 120, 3817-3818. (h) Everaere, K.; Carpenter, J .-F.; Mortreux, A,;
Bulliard, M. Tetrahedron: Asymmetry 1998, 9, 2971-2974.
(6) Crystal structure analysis of 2a ‚H2O: C23H36ClN2O3SRh, Mt ) 558.97,
triclinic, space group P1 (#1), a ) 11.353(2) Å, b ) 13.086(2) Å, c ) 9.123(2)
Å, R ) 92.19(2)°, â ) 93.68(1)°, γ ) 100.93(1)°, V ) 1326.2(4) Å3, Z ) 2, Dc
) 1.40 g/cm3, µ(Mo KR) ) 8.48 cm-1, R (Rw) ) 0.040 (0.043) for 5574 observed
reflections (I > 3.00σ(I)). 4a ‚H2O: C23H36ClN2O3SIr, Mt ) 648.28, triclinic,
space group P1 (#1), a ) 11.365(4) Å, b ) 13.042(7) Å, c ) 9.162(4) Å, R )
92.07(5)°, â ) 93.99(4)°, γ ) 100.85(4)°, V ) 1328(1) Å3, Z ) 2, Dc ) 1.62
g/cm3, µ(Mo KR) ) 52.41 cm-1, R (Rw) ) 0.062 (0.065) for 5167 observed
reflections (I > 3.00σ(I)). After submission of this paper, a report from Tani
describing related work on TsDPEN complexes of Rh and Ir appeared.
Mashima, K.; Abe, T.; Tani, K. Chem. Lett.1998, 1199-1200.
(1) Noyori, R. Asymmetric Catalysis in Organic Synthesis; J ohn Wiley
& Sons: New York, 1994; Chapter 2.
(2) (a) Mu¨ller, D.; Umbricht, G.: Weber, B.; Pfaltz, A. Helv. Chim. Acta
1991, 74, 232-240. (b) Chowdhury, R. L.; Ba¨ckvall, J .-E. J . Chem. Soc.,
Chem. Commun. 1991, 1063-1064. (c) Zassinovich, G.; Mestroni, G. Chem.
Rev. 1992, 92, 1051-1069. (d) Gamez, P.; Fache, F.; Mangeney, P.; Lemaire,
M. Tetrahedron Lett. 1993, 34, 6897-6898. (e) Geneˆt, J .-P.; Ratovelo-
manana-Vidal, V.; Pinel, C. Synlett 1993, 478-480. (f) Evans, D. A.; Nelson,
S. G.; Gagne´, M. R.; Muci, A. R. J . Am. Chem. Soc. 1993, 115, 9800-9801.
(g) Gamez, P.; Fache, F.; Lemaire, M. Tetrahedron: Asymmetry 1995, 6,
705-718. (h) Langer, T.; Helmchen, G. Tetrahedron Lett. 1996, 37, 1381-
1384. (i) J iang, Y.; J iang, Q.; Zhu, G.; Zhang, X. Tetrahedron Lett. 1997,
38, 215-218. (j) J iang, Q.; Plew, D. V.; Murtuza, S.; Zhang, X. Tetrahedron
Lett. 1997, 37, 797-800. (k) Touchard, F.; Gamez, P.; Fache, F.; Lemaire,
M. Tetrahedron Lett. 1997, 38, 2275-2278. (l) Barbaro, P.; Bianchini, C.;
Togni, A. Organometallics 1997, 16, 3004-3014. (m) Sammakia, T.;
Stangeland, E. L. J . Org. Chem. 1997, 62, 6104-6105.
(3) (a) Hashiguchi, S.; Fujii, A.; Takehara, J .; Ikariya, T.; Noyori, R. J .
Am. Chem. Soc. 1995, 117, 7562-7563. (b) Takehara, J .; Hashiguchi, S.;
Fujii, A.; Inoue, S.; Ikariya, T.; Noyori, R. J . Chem. Soc., Chem. Commun.
1996, 233-234. (c) Gao, J .-X.; Ikariya, T.; Noyori, R. Organometallics 1996,
15, 1087-1089. (d) Fujii, A.; Hashiguchi, S.; Uematsu, N.; Ikariya, T.;
Noyori, R. J . Am. Chem. Soc. 1996, 118, 2521-2522. (e) Uematsu, N.; Fujii,
A.; Hashiguchi, S.; Ikariya, T.; Noyori, R. J . Am. Chem. Soc. 1996, 118,
4916-4917. (f) Haack, K.-J .; Hashiguchi, S.; Fujii, A.; Ikariya, T.; Noyori,
R. Angew. Chem., Int. Ed. Engl. 1997, 36, 285-288. (g) Hashiguchi, S.; Fujii,
A.; Haack, K.-J .; Matsumura, K.; Ikariya, T.; Noyori, R. Angew. Chem., Int.
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10.1021/jo990213a CCC: $18.00 © 1999 American Chemical Society
Published on Web 03/12/1999

Communications
J . Org. Chem., Vol. 64, No. 7, 1999 2187
Ta ble 1. Asym m etr ic Tr a n sfer Hyd r ogen a tion of
Acetop h en on es Ca ta lyzed by P r efor m ed Ch ir a l Ca ta lysts
a n d KO-t-Bu System in 2-P r op a n ola
convnb eec
cat.
ketone
time (h)
(%)
(%) confignd
(R,R)-1a 6a
(R,R)-2a 6a
(R,R)-3a 6a
(R,R)-4a 6a
(R,R)-2a m-6b
(R,R)-2a m-6be
(R,R)-2a m-6bf
(R,R)-2a m-6b (1M)
(R,R)-1a m-6b
(R,R)-4a m-6b
(R,R)-2a o-6b
(R,R)-2a o-6c
(R,R)-2a o-6d
(R,R)-2a p-6e
(R,R)-2a p-6f
(R,R)-2a 1-tetralone
(R,R)-2a 1-indanone
(R,R)-2a 1′-acetonaphthone
12
12
12
12
12
24
66
12
6
24
12
12
24
24
24
24
24
48
92
85
14
94
97
90
96
97
97
96
80
90
94
96
91
94
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
R
36
>99
>99
90
95
>99
99
>99
97
20
58
22
53
43
48
>99
>99
F igu r e 1. ORTEP view of Cp*RhCl[(1R,2R)-N-(p-toluenesulfo-
nyl)-1,2-cyclohexanediamine) (2a ). One crystal water molecule has
been omitted for the sake of clarity. Selected bond lengths (Å):
Rh1-Cl1, 2.447(2); Rh1-N1, 2.152(7); Rh1-N2, 2.116(7); Cl1-
H1, 2.70. Selevted bond angles (deg): Cl1-Rh1-N1, 89.9(2); Cl1-
Rh1-N2, 83.3(2); N1-Rh1-N2, 78.1(3).
95g
97g
87
a
The reaction was carried out at 30 °C using a 0.1 M solution
of the ketone in 2-propanol. Ketone/cat./KO-t-Bu ) 200:1:1.2.
Conversion was determined by GLC. c Determined by GLC
b
d
analysis using a Chirasil-DEX CB (25m). Determined from the
the reaction of 4a with 1 equiv of NaOH in 2-propanol gave
Cp*IrH[(R,R)-Tscydn] (4b) as a single stereoisomer.7 The
complex 4b readily reacted with acetone to provide quanti-
tatively the 5-coordinate amide complex 4c where the amine
ligand is deprotonated.7 The single-crystal X-ray crystal-
lographic analysis of 4b indicates that it has a structure
similar to that of the chloride complex 4a .
sign of rotation of the isolated product. e The reaction with S/C )
500. f The reaction with S/C ) 1000. Determined by HPLC
g
analysis using a Daicel Chiralcel OB column.
attain high catalysis performance the reaction using a 0.1
M solution is recommended. The structures and electronic
properties of the ketonic substrates significantly affect the
outcomes of the reactions (Table 1). The reduction of ac-
etophenones with electron-withdrawing substituents, 6b or
6c, proceeds rapidly to the corresponding chiral alcohols with
excellent yield and high ee. Electron-donating substituents
resulted in a slower reaction as expected but with a high
enantioselectivity. The bulkiness of the R2 group in 6g
caused a strong retardation of the reaction, giving the
product with a low ee (1% conv, 29% ee). The cyclic
substrates, 1-tetralone and 1-indanone, are also converted
to the corresponding alcohols with high enantiomeric puri-
ties and in moderate yields.
Noticeably, both the isolable Ir hydride complex (4b)7 and
the amide complex (4c)7 catalyzed the asymmetric transfer
hydrogenation of 6b in 2-propanol without any bases to give
(R)-1-(m-trifluoromethylphenyl)ethanol with the same enan-
tioselectivity in comparison to the catalyst system consisting
of 4a and KO-t-Bu (S/C ) 500, 12 h reaction: 95% conver-
sion, 95% ee with 4b, 83% conversion, 94% ee with 4c; 87%
conversion, 94% ee with 4a /KO-t-Bu). Successful isolation
of the complex 4b or 4c as well as their catalytic performance
confirms that this asymmetric reduction takes place by the
action of the hydride or amide complex as the catalyst or
intermediate, as observed in the same reaction promoted by
the chiral Ru complex system.3f
These well-defined Rh and Ir complexes effect the asym-
metric transfer hydrogenation of aromatic ketones to the
corresponding chiral alcohols in 2-propanol containing a
base. The reaction of acetophenone (6a ) (0.1 M) in 2-propanol
containing (R,R)-2a and KO-t-Bu at 30 °C (ketone/2a /KO-
t-Bu ) 200:1:1.2) for 12 h gave (R)-1-phenylethanol with 97%
ee in 85% yield. The rate and enantioselectivity of the
reaction are strongly affected by the central metals and the
structure of the chiral diamine ligands (Table 1). The Rh
complex with TsCYDN is the better catalyst in terms of the
rate and enantioselectivity in comparison to the Ir complex
with the same amine. The TsCYDN complexes provide
higher reactivity than the TsDPEN complexes. The analo-
gous preformed chiral Ru complex (1a ) with the TsDPEN
ligand has a somewhat higher reactivity with a comparable
to lower enantioselectivity (92% yield, 94% ee) for reduction
of 6a . m-(Trifluoromethyl)acetophenone (6b) (substrate/
catalyst ratio (S/C) ) 200-500) was readily reduced almost
quantitatively to an intermediate of the fungicide, (R)-1-(m-
trifluoromethylphenyl)ethanol, with 97% ee. A reaction using
a 0.1 M solution with a S/C of 1000 gave the optically active
alcohol in a good yield without a significant deterioration of
the enantiomeric purity. Since the transfer hydrogenation
of ketone with 2-propanol is reversible, the reaction using a
1 M solution of 6b resulted in a decrease in the stereose-
lectivity to ca. 80% ee after 95% conversion for 12 h. To
(7) Ir amide complex 4c was obtained quantitatively by a reaction of Ir
hydride 4b with acetone. A yellow crystalline complex is obtained by
recrystallization from toluene. The direct conversion of 4a to 4c in toluene
containing a base caused a lower yield. The details of the structures and
chemical properties of 4b and 4c will be reported soon. 4b: 1H NMR (270
MHz, toluene-d8) δ -10.4 (s, 1H, Ir-H), 0.8-2.4 (11H, cyclohexane ring
protons plus 1H, NH), 1.72 (s, 15H, C5(CH3)5), 2.08 (s, 3H, CH3 of Ts), 3.18
(m, 1H, NH), 7.0, 8.07 (4H, aromatic ring protons). The crystallization from
THF provides pale yellow crystals suitable for X-ray analysis. Crystal
structure analysis of 4b‚2THF: C31H51N2O4SIr, Mt ) 740.04, orthorhombic,
space group P212121 (#19), a ) 10.170(1) Å, b ) 14.969(1) Å, c ) 22.454(3)
Å, V ) 3418.1(6) Å3, Z ) 4, Dc ) 1.44 g/cm3, µ(Mo KR) ) 40.2 cm-1, R (Rw)
) 0.047 (0.066) for 2676 observed reflections (I > 3.00σ(I)). 4c: 1H NMR
(270 MHz, acetone-d6) δ 0.7-2.7 (10H, cyclohexane ring protons), 1.70 (s,
15H, C5(CH3)5), 2.35 (s, 3H, CH3 of Ts), 5.10 (br, 1H, NH), 7.21, 7.74 (4H,
aromatic ring protons).
Ack n ow led gm en t. We thank Professor Takeshi Oh-
kuma of Nagoya University and Drs. Shohei Hashiguchi
and Karl J . Haack of the J ST ERATO Project for helpful
discussions and Dr. Motoo Shiro of Rigaku Corporation for
the single-crystal X-ray analysis of 4b.
Su p p or tin g In for m a tion Ava ila ble: The [R]D values of the
reaction products, the experimental procedure for the transfer
hydrogenation reaction of m-6b, and the single-crystal X-ray
information for 2a and 4a .
J O990213A