Heterogeneous enantioselective hydrogenation of aromatic ketones catalyzed by cinchona- and phosphine-modified iridium catalysts

Article abstract of DOI:10.1002/anie.200801809

(Chemical Equation Presented) Catalyst support: The first highly enantioselective heterogeneous hydrogenation of aromatic ketones catalyzed by Ir/SiO₂ stabilized with Ph₃P and modified by a chiral diamine derived from a cinchona alkaloid is described (see scheme). The reaction can be employed for the reduction of a broad range of aromatic ketones to the corresponding alcohols with high enantioselectivity.

Full text of DOI:10.1002/anie.200801809

Communications
DOI: 10.1002/anie.200801809
Heterogeneous Catalysis
Heterogeneous Enantioselective Hydrogenation of Aromatic Ketones
Catalyzed by Cinchona- and Phosphine-Modified Iridium Catalysts**
He-yan Jiang, Chao-fen Yang, Chun Li, Hai-yan Fu, Hua Chen,* Rui-xiang Li, and Xian-jun Li
Dedicated to the Catalysis Society of Japan on the occasion of the 50th anniversary
Heterogeneous catalytic systems for asymmetric reactions are
fascinating because of their potential in synthetic applica-
tions.[1] However, because of the high substrate specificity of
these catalysts, the complexity of the task at hand, and the
difficulties in understanding and designing the catalytic
reactions, there have been just three established systems
reported.[1a] One system identified for asymmetric hydro-
genation is the cinchona-modified Pt/Al2O3 for asymmetric
hydrogenation of a-keto esters, which was developed by Orito
et al. in 1979.[2] Baiker et al. successfully used this catalyst in
the asymmetric hydrogenation of activated aromatic
ketones.[3] However, when considering the asymmetric hydro-
genation of simple aromatic ketones and derivatives, which
are among the most fundamental subjects in modern synthetic
chemistry, few successful heterogeneous catalytic examples
are reported.
Chiral modifiers are the origin of the enantioselectivity in
most heterogeneous catalytic reactions, and natural cinchona
alkaloids and their derivatives have been widely used as
versatile chiral catalysts, ligands, column packing, and chiral
shift reagents.[4] Two of the three most well-known heteroge-
neous catalytic systems in asymmetric reactions are based on
natural cinchona alkaloids and their derivatives as the chiral
modifiers.[2,5] Stabilizers, which are widely used in preparing
nanometal catalysts, including amines,[6] phosphines,[7] and
thiols,[8] have been gradually introduced into supported
catalysts in recent years. We previously reported polyvinyl-
pyrrolidone (PVP) and cinchona-stabilized Rh in the asym-
metric hydrogenation of a-keto esters, in which moderate to
good enantioselectivities were obtained.[9] Meanwhile, little
attention has been paid to the preparation of supported metal
catalysts stabilized by phosphines. Reported herein is a Ph3P-
stabilized Ir/SiO2 catalyst system modified by a chiral
diamine, derived from cinchona alkaloids, for the asymmetric
hydrogenation of simple aromatic ketones and their deriva-
tives; the results are compared to known homogeneous
catalysts.[10] To the best of our knowledge, this is the first
report of the asymmetric hydrogenation of simple aromatic
ketones with a greater than 95% ee by using a new hetero-
geneous catalyst. This report is also the first successful
example of the asymmetric hydrogenation of simple aromatic
ketones employing Ir and H2.
The high-resolution transmission electron microscopy
(HRTEM) picture (Figure 1 in the Supporting Information)
of 3%Ir/SiO2/2tpp (tpp = triphenylphosphine) showed that Ir
is highly dispersed on the SiO2 as an amorphous agglomerate.
The X-ray photoelectron spectroscopy (XPS) analysis indi-
cated that the metal component is present in a reduced state
(Ir 4f7/2 core level centered at 61.6 eV) compared to Ir0 (Ir 4f7/2
core level centered at 60.8 eV),[11] and the binding energy
(103.5 eV) of Si2p is similar to the expected value (103.4 eV)
for the corresponding SiO2.[12] The full range XPS spectra
indicated that the amount of Ir supported on the SiO2 is
3% wt/wt. The catalysts are remarkably stable in the solid
state and can be stored open to air.
IR and 31P solid state NMR (31PMAS NMR) spectra are
effective for the investigation of the mutual ligand–metal–
support interactions of solid catalysts.[13] Information on the
interaction between the metal and the phosphine was first
confirmed by FTIR methods in which the red shift of the
À1
À
P C6H5 deformation around 1434 cm in 3%Ir/SiO2/2tpp is
an indication of the coordination of PPh3 to the metal.
Interaction between the cinchona alkaloid and the metal was
also confirmed by FTIR analysis in which the blue shift of the
À1
À
N H deformation around 3366 cm in 3%Ir/SiO2/2tpp/
diamine 2 is an indication of the coordination of the amine
with the metal. Furthermore, the interactions between PPh3,
Ir, 2, and SiO2 were detected by 31PMAS NMR spectroscopy
(Figure 1); the broad signal at d = À5.4 ppm in Figure 1a was
assigned to the PPh3 supported on the SiO2 on the basis of
literature reports.[13a] The broad signal at d = 37.4 ppm may be
attributed to a strong P···Si interaction on acidic SiO2
(Figure 1a), which is similar to phenomena observed in
previous reports.[13] The broad signals at d = 8.2 ppm and d =
26.0 ppm in Figure 1c are new, and appear during the catalyst
(3%Ir/SiO2/2tpp) preparation, whereas the signal for the
PPh3 supported on SiO2 disappeared and the signal for the
P···Si interaction was enhanced. When diamine 2 was added to
the 3%Ir/SiO2/2tpp catalyst (Figure 1d), two new signals
appeared (d = 13.5 and 30.3 ppm) and the signal of the P···Si
[*] H.-y. Jiang, C.-f. Yang, C. Li, H.-y. Fu, Prof. H. Chen, Prof. R.-x. Li,
Prof. X.-j. Li
Key Lab of Green Chemistry and Technology, Ministry of Education,
The Institute of Homogeneous Catalysis, College of Chemistry,
Sichuan University
No. 29 Wang jiang Road, Chengdu 610064 (PR China)
Fax: (+86)28-8541-2904
E-mail: scuhchen@163.com
Homepage: http://chem.scu.edu.cn/professor/chenhua.htm
[**] This work was financially supported by the National Natural Science
Foundation of China (No. 20272037) and the Doctor’s Foundation
of Education Ministry of China (No. 20030610022). The authors
thank Prof. Xian-Deng Hou for his kind help during the preparation
of the manuscript.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.200801809.
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Scheme 1. Modifiers used and the general reaction.
phosphino)butane
(diop),
2,2’-bis(diphenylphosphino-
methyl)-1,1’-biphenyl (bisbi) and (S)-2,2’-bis(di-4-tolylphos-
phino)-1,1’-binaphthyl (tolbinap), were tested, however, none
of them were better than the simple achiral PPh3. The highest
activity and enantioselectivity was obtained when the initial
molar ratio of PPh3 to Ir used in the preparation of the
catalyst was 2:1 (the actual PPh3/Ir ratio on the SiO2 support is
1.9:1, which was measured by ICP-AES methods). Increasing
or decreasing the ratio of PPh3 to Ir was unfavorable to both
the activity and the enantioselectivity. Methanol is the best
choice for a solvent as both low activity and poor enantio-
selectivity were observed in other solvents. Similar to
homogeneous reactions[10] and some heterogeneous reaction-
s,[9e,14a,15] a base is necessary to accelerate the reaction. The
addition of different bases, such as tBuOK, LiOH, NaOH, or
KOH, can enhance both the activity and the enantioselectiv-
ity. For the alkali metal hydroxides both the activity and the
enantioselectivity decrease in the order of Li+ > Na+ > K+.
The addition of both modifier 2 and LiOH greatly enhanced
the activity and enantioselectivity (Table 1, entry 2). A high
concentration of the modifier is needed for simple aromatic
ketone asymmetric hydrogenation; a similar observation was
reported in recent work by Reyes and co-workers[16]. By using
1 mol% (compared to the supported Ir) of chiral diamine 2,
the enantioselectivity was maintained during the asymmetric
hydrogenation at an elevated temperature and a prolonged
reaction time (408C, 20 h, 36% conversion and 66% ee).
Possibly, the sterically hindered diamine 2 prefers the base
with the smaller metal cation to produce higher activity and
enantioselectivity. In the absence of LiOH, the conversion
was only 2% with 31% ee at 308C for three hours. By raising
the reaction temperature and prolonging the reaction time
(408C, 20 h), the reaction proceeds with 16% conversion and
54% ee. These results suggest that a proper stabilizer, molar
ratio of P/Ir, solvent, and combination of chiral diamine and
LiOH are helpful for the formation of the catalytic species
and the resulting chiral induction.
Figure 1. 31PMAS NMR spectra of a) PPh3/SiO2, c) 3%Ir/SiO2/2tpp,
and d) 3%Ir/SiO2/2tpp/diamine 2; and 31P NMR spectra of b) [{Ir-
(cod)Cl}2]/2tpp/diamine 2. cod=cycloocta-1,5-diene.
interaction weakened. The above results suggest that the
broad signals at d = 8.2 ppm and 26.0 ppm in Figure 1c
represent the coordination between PPh3 and Ir on the
SiO2, and the new signals at d = 13.5 and 30.3 ppm in
Figure 1d are valuable hints about the coordination between
diamine 2 and Ir. In comparing these signals with those of the
homogeneous [{Ir(cod)Cl}2]/2tpp/diamine 2 catalyst (Fig-
ure 1b), the PPh3–Ir coordination around 26.0 ppm in Fig-
ures 1c and d might be similar to the PPh3–Ir coordination in
homogeneous [{Ir(cod)Cl}2]/2tpp/diamine 2 catalyst.
Asymmetric hydrogenation of aromatic ketones was
performed in a 20 mL stainless steel autoclave with a
magnetic stirr bar, by using chiral diamine 1 (9-amino(9-
deoxy)epicinchonine) and 2 (9-amino(9-deoxy)epicinchoni-
dine) as modifiers, which are derived from natural cinchona
alkaloids (Scheme 1). Chiral modifier 2 was used to test the
effect of the different reaction factors on the asymmetric
hydrogenation of acetophenone. The stabilizer (PPh3) is very
important in this system; without the stabilizer, the hydro-
genation resulted in a conversion as low as 11% and an
ee value of 9%. Classically modified 3%Ir/SiO2 catalyst with
tpp and chiral modifier 2 gave a 17% conversion and 52%
enantioselectivity (408C, 20 h). These results indicate that
phosphine not only stabilized the metal particles in the
preparation of the catalyst, but also served to additionally
modify the supported metal with diamine in the asymmetric
hydrogenation. Since the properties of the stabilizers greatly
influence the particle size and dispersion of the reduced metal
in the catalyst,[5a] phosphines, such as tris(4-methoxyphenyl)-
phosphine (motpp), tris(4-trifluoromethylphenyl)phosphine
(tftpp), tris(sodium-m-sulfonatophenyl)phosphine (tppts),
1,2-bis(diphenylphosphinomethyl)benzene (bdpx), (S,S)-
(+)-2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis(diphenyl-
For the cinchona-modified Pt/Al2O3 system, it was found
that a small change in the structure of modifier led to an
interesting influence on the activity, the enantioselectivity,
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Communications
Table 1: Enantioselective hydrogenation of aromatic ketones catalyzed
solution to from a soluble complex that has catalytic activity.
There are few successful examples of homogeneous catalysts
employing Ir with H2 in the presence of both a phosphine and
an amine are reported, but there are some successful
examples reported for transfer hydrogenation.[19] For com-
parison to this work, homogeneous catalysts, formed in situ,
were investigated for the hydrogenation and poor results were
obtained. For example, the homogeneous Ir/2tpp/diamine 2
catalyst gave 100% conversion and 45% ee at 308C after
3 hours, the homogeneous Ir/2tppts/diamine 2 catalyst ach-
ieved 98% conversion and 18% ee, and the homogeneous Ir/
bisbi/diamine 2 catalyst achieved 60% conversion and
36% ee (for details of the homogeneous catalytic experiment
see the Supporting Information). The conventional filtering
test[9e,14] was employed to investigate the catalyst leaching. At
the end of the hydrogenation reaction with chiral modifier 2,
the solution and the catalyst were separated by using high-
speed centrifugation under an argon atmosphere, and both
the solution and the catalyst were used for another hydro-
genation reaction with acetophenone. The solution had no
catalytic activity after when fresh substrate was introduced,
and the leaching of Ir and PPh3 from the 3%Ir/SiO2/2tpp
catalyst into the solution was measured by ICP-AES methods
to show that only 0.12% Ir and 0.57% PPh3 were detected in
the liquid phase after the first hydrogenation of acetophe-
none. This small amount of metal leaching is ascribed to an
equilibrium between the soluble and the bound metal that
commonly exists in supported heterogeneous catalyst.[20]
Similar to the work reported by Bujoli and co-workers,[20a]
the molar ratio of PPh3/Ir leached into solution is large (9:1) ,
which poisoned the Ir which leached into the solution. A
similar poisoning phenomenon was observed in other experi-
ments (Figure 3 in the Supporting Information and a previous
report).[20b] Both the small amount of metal leaching and the
excess PPh3 (PPh3/Ir= 9:1) leached into the solution result in
no observed catalytic activity upon addition of fresh substrate.
However, the recovered catalyst maintained its activity,
although the activity and enantioselectivity decreased in
some content. Furthermore, mercury-poisoning experiments
were run as they can selectively poison metal nanoparticles,
by forming an amalgam with mercury, to help distinguish
between homogeneous and heterogeneous catalysts.[21] In
such an experiment for our system, the conversion in the
presence of modifier 2 was 20% after the initial 15 minutes;
mercury was then added under argon atmosphere and the
reaction was completely terminated as evidenced by no
change in the conversion (20.7%) after an additional reaction
time of one hour. Additionally, according to the graph of the
conversion versus time over the period of 0–30 minutes for
the hydrogenation, the conversion of acetophenone increased
linearly, showing no induction period for our system, proving
that this catalyst does not convert into other catalytically
active species. All the results above strongly support proposal
that the reaction progresses under heterogeneous catalysis
rather than homogeneous catalysis.
by 3%Ir/phosphine/SiO2/diamine system (see Scheme 1).[a]
Entry Substrate Diamine t [h] Yield [%] ee [%] Config.[b]
1
2
3
4
5
6
7
8
a
a
a
b
b
c
c
d
d
e
e
e
f
1
2
1[c]
1
2
1
2
1
2
1
1
2
1
2
1
1
2
1
2
1
10
3
6
10
3
10
3
10
3
10
20
3
10
3
10
10
3
>99
>99
>99
44
96
80
>99
83
>99
55
>99
99
60
96
33
75
97
21
97
48
88
74
86
86
77
96
86
92
90
94
95
86
81
83
75
87
76
86
75
52
S
R
S
S
R
S
R
S
R
S
S
R
S
R
S
S
R
S
R
S
9
10
11
12
13
14
15
16
17
18
19
20
f
g
h
h
i
i
j
10
3
10
[a] Reaction was carried out at 308C for modifier 2 and 408C for modifier
1. Substrate: in a 2 mL methanol solution at [0.313m], PH :6.0MPa.
2
Substrate/Ir/diamine=200:1:2, [LiOH]=0.125 molLÀ1. Products were
analyzed by a GC instrument with an FID detector and b-DEX120
capillary column. [b] Determined by sign of rotation. [c] The double bond
of modifier 1 was hydrogenated.
and the configuration of the product,[17] providing useful
information for understanding the reaction mechanism; for
example, when DHCD (10, 11-dihydrocinchonidine) is used
as a modifier in the hydrogenation of a-keto esters, the
catalyst activity and enantioselectivity are higher than those
obtained with cinchonidine (CD). Modifiers containing a
small alkoxy group (methoxy, ethoxy) gave the same enan-
tiomer in similar excess to that obtained with CD. The
enantioselectivity decreases rapidly with the increasing bulki-
ness of the ether group, and in some cases even the opposite
enantiomer is formed with good ee values.[18] In our system,
when the double bond in modifier 1 was hydrogenated, the
reaction rate was enhanced for the hydrogenation of aceto-
phenone, but the enantioselectivity was slightly decreased
(Table 1, entries 1 and 3). This result is an indication that the
double bond in modifier 1 is helpful in creating a favorable
steric environment for enantioselectivity. To our surprise,
when 9-amino(9-deoxy)epiquinine was used as a modifier in
the hydrogenation of acetophenone, the reaction progressed
very slowly with a low enantioselectivity even under elevated
reaction temperatures and prolonged reaction times (308C,
20 h, 3% conversion and 25% ee; 408C, 20 h, 9% conversion
in 40% ee). This indicates the high specific correlation
between the modifier and substrate. Other modifiers, such
as cinchonine, cinchonidine, and quinine, were tested, and the
amine group in the nine-position of the modifier is essential
(for details of different reaction parameters affecting the
hydrogenation see the Supporting Information)
Some representative examples are listed in Table 1 for the
asymmetric hydrogenation of aromatic ketones catalyzed by
Ph3P stabilized Ir/SiO2 modified by diamine 1 or 2. The extent
of the enantioselectivity appears to be delicately influenced
Because of the similarity of our Ir catalyst to the Ru/
phosphine/diamine catalsyt in a homogeneous system, it is
important to clarify whether the Ir leached into the reaction
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2007, 40, 1348; d) A. Tungler, E. Sipos, V. Hadac, Arkivoc 2004,
by the structure of the diamine auxiliary as well as the
substituent in the substrate. In general, modifier 1 shows
better enantioselectivity but lower activity than modifier 2.
The use of the S diamine affords the R-configurated alcohol
product, whereas the R diamine gives the S-configured
alcohol. Ortho substituents on acetophenone do not improve
the activity of the asymmetric hydrogenation because of the
steric bulk, but the activity increases with the decreasing
electronegativity of the halogen (Table 1, entries 4–9). Our
system is smilar to the cinchona-modified Pt/Al2O3 system[1]
in that the enantioselectivitiy gradually increases as the
reaction progresses (Table 1, entries 10 and 11). The highest
enantiomeric excess was obtained for the hydrogenation of
2’-chloroacetophenone by using diamine 1 as the chiral
modifier (Table 1, entry 6). Other substrates were also
tested and it was found that when the substituent is in the
meta or para position (Table 1, entry 15–17), the degree of the
enantioselection was obviously decreased in comparison to
the ortho-substituted counterparts. The enantioselectivity
also decreased by increasing the bulkiness of the alkyl
group from methyl or primary alkyl to isopropyl (Table 1,
entries 1 and 2, and 18–20). The effect of the steric bulk and
the electronic nature of the substrate influence the activity
and the enantioselectivity of the reaction.
223; e) D. Y. Murzin, P. Maki-Arvela, E. Toukoniitty, T. Salmi,
Catal. Rev. Sci. Eng. 2005, 47, 175; f) M. Heitbaum, F. Glorius, I.
Escher, Angew. Chem. 2006, 118, 4850; Angew. Chem. Int. Ed.
2006, 45, 4732.
[2] a) Y. Orito, S. Imai, S. Niwa, J. Chem. Soc. Jpn. 1979, 1118; b) Y.
Orito, S. Imai, S. Niwa, J. Chem. Soc. Jpn. 1980, 670.
[3] a) A. Vargas, D. Ferri, N. Bonalumi, T. Mallat, A. Baiker, Angew.
Chem. 2007, 119, 3979; Angew. Chem. Int. Ed. 2007, 46, 3905;
b) M. von Arx, T. Mallat, A. Baiker in Supported Catalysts and
Their Applications (Eds.: D. C. Sherrington, A. P. Kybett), The
Royal Society of Chemistry, Cambridge, 2001, p. 247; c) T.
Mallat, M. Bodmer, A. Baiker, Catal. Lett. 1997, 44, 95; d) T.
Varga, K. Felfꢀldi, P. Forgꢁ, M. Bartꢁk, J. Mol. Catal. A 2004,
216, 181.
[4] K. K. Acprzak, J. Gawroꢂski, Synthesis 2001, 7, 961.
[5] a) Y. Izumi, Adv. Catal. 1983, 32, 215; b) A. Tai, T. Sugimura in
Chiral Catalyst Immobilization and Recycling (Eds.: D. E.
De Vos, I. F. J. Vankelecom, P. A. Jacobs), Wiley-VCH, Wein-
heim, 2000, p. 173; c) Y. Nitta, J. Watanabe, T. Okuyama, T.
Sugimura, J. Catal. 2005, 236, 164; d) W. R. Huck, T. Mallat, A.
Baiker, New J. Chem. 2002, 26, 6.
[6] D. V. Leff, L. Brandt, J. R. Heath, Langmuir 1996, 12, 4723.
[7] a) M. Tamura, H. Fujihara, J. Am. Chem. Soc. 2003, 125, 15742;
b) S. Jansat, M. Gomez, K. Philippot, G. Muller, E. Guiu, C.
Claver, S. Castillon, B. Chaudret, J. Am. Chem. Soc. 2004, 126,
1592; c) G. Schmid, Clusters and Colloids; VCH, Weinheim,
1994; d) G. Schmid, R. Pfeil, R. Boese, F. Bandermann, S. Meyer,
G. H. M. Calis, J. W. A. van der Velden, Chem. Ber. 1981, 114,
3634.
[8] a) M. Brust, M. Walker, D. Bethell, D. J. Schiffrin, R. Whyman, J.
Chem. Soc. Chem. Commun. 1994, 801; b) A. C. Templeton,
W. P. Wuelfing, R. W. Murray, Acc. Chem. Res. 2000, 33, 27; c) K.
Hata, H. Fujihara, Chem. Commun. 2002, 2714.
[9] a) Y. L. Huang, J. R. Chen, H. Chen, R. X. Li, Y. Z. Li, L.-e. Min,
X. J. Li, J. Mol. Catal. A. 2001, 170, 143; b) Y. L. Huang, Y. Z. Li,
J. Y. Hu, P. M. Cheng, H. Chen, R. X. Li, X. J. Li, C. W. Yip,
A. S. C. Chan, J. Mol. Catal. A 2002, 189, 219; c) H. X. Ma, H.
Chen, Q. Zhang, X. J. Li, J. Mol. Catal. A. 2003, 196, 131; d) W.
Xiong, H. X. Ma, Y. Y. Hong, H. Chen, X. J. Li, Tetrahedron:
Asymmetry 2005, 16, 1449; e) D. R. Liu, W. Xiong, G. Y. Fang, H.
Chen, R. X. Li, X. J. Li, Appl. Catal. A 2008, 339, 93.
[10] T. Ohkuma, H. Ooka, S. Hashiguchi, T. Ikariya, R. Noyori, J.
Am. Chem. Soc. 1995, 117, 2675.
[11] a) B. Pawelec, R. M. Navarro, J. M. Campos-Martin, A. Lꢁpe-
z Agudo, P. T. Vasudevan, J. L. G. Fierro, Catal. Today 2003, 86,
73; b) P. Castaꢂo, B. Pawelec, J. L. G. Fierro, J. M. Arandes, J.
Bilbao, Appl. Catal. A 2006, 315, 101.
[12] T. Marzialetti, J. L. G. Fierro, P. Reyes, Catal. Today 2005, 107–
108, 235.
In conclusion we demonstrated the facile preparation of a
supported iridium catalyst which is stabilized by PPh3. When
modified by a chiral diamine, derived from cinchona alka-
loids, this catalyst exhibits a high activity and high enantio-
selectivity for the hydrogenation of simple aromatic ketones,
especially for ortho-substituted aromatic ketones. The work
reported herein provides a new direction for asymmetric
synthesis. Additional work is currently in progress in this and
related areas.
Experimental Section
Ph3P stabilized Ir/SiO2 catalyst was prepared with a slight modifica-
tion to our previous reported method.[9] Under an argon atmosphere,
a solution of SiO2 (1.0 g, the average pore size is 4.5 nm, SBET
=
135.9 m2 gÀ1), H2IrCl6 (0.168 mmol) and PPh3 (0.336 mmol) in
iPrOH (30 mL) was stirred at room temperature for 24 h, after
which formaldehyde (5 mL) was added and the mixture heated at
1108C with stirring for 5 h. The mixture was then cooled to room
temperature and the solid was then separated and dried under
vacuum at room temperature for 6 h to give the catalyst 3%Ir/SiO2/
2tpp (the average pore size is 3.9 nm, SBET = 125.6 m2 gÀ1. The
reduction of the average pore size and SBET indicates the attachment
of the Ir-tpp to SiO2 surface). Similarly, other catalysts, with different
stabilizers, were prepared by the same procedure.
[13] a) L. Yan, Y. J. Ding, H. J. Zhu, J. M. Xiong, T. Wang, Z. D. Pan,
L. W. Lin, J. Mol. Catal. A 2005, 234, 1; b) D. F. Han, X. H. Li,
H. D. Zhang, Z. M. Liu, G. S. Hu, C. Li, J. Mol. Catal. A 2008,
283, 15; c) K. V. Kovtunov, I. E. Beck, V. I. Bukhtiyarov, I. V.
Koptyug, Angew. Chem. 2008, 120, 1514; Angew. Chem. Int. Ed.
2008, 47, 1492.
Received: April 17, 2008
Revised: July 7, 2008
Published online: August 8, 2008
[14] a) H. Y. Chen, J. M. Hao, H. J. Wang, C. Y. Xi, X. C. Meng, S. X.
Cai, F. Y. Zhao, J. Mol. Catal. A 2007, 278, 6; b) R. A. Sheldon,
M. Wallau, I. W. C. E. Arends, U. Schuchardt, Acc. Chem. Res.
1998, 31, 485.
[15] A. Perosa, P. Tundo, M. Selva, J. Mol. Catal. A 2002, 180, 169.
[16] T. Marzialetti, M. Oportus, D. Ruiz, J. L. G. Fierro, P. Reyes,
Catal. Today 2008, 133–135, 711.
Keywords: alkaloids · asymmetric catalysis · iridium · ketones ·
.
supported catalysts
[17] a) A. Pfaltz, T. Heinz, Top. Catal. 1997, 4, 229; b) H. U. Blaser,
H. P. Jalett, W. Lottenbach, M. Studer, J. Am. Chem. Soc. 2000,
122, 12675.
[1] a) M. Studer, H. U. Blaser, C. Exner, Adv. Synth. Catal. 2003,
345, 45; b) T. Mallat, E. Orglmeister, A. Baiker, Chem. Rev.
2007, 107, 4863; c) H. U. Blaser, M. Studer, Acc. Chem. Res.
Angew. Chem. Int. Ed. 2008, 47, 9240 –9244
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org 9243

Communications
[18] F. Hoxha, L. Kꢀnigsmann, A. Vargas, D. Ferri, T. Mallat, A.
Ed. 2006, 45, 7063; d) Y. Gu, C. Ogawa, J. Kobayashi, Y. Mori, S.
Kobayashi, Angew. Chem. 2006, 118, 7375; Angew. Chem. Int.
Ed. 2006, 45, 7217; e) B. H. Lipshutz, B. R. Taft, Angew. Chem.
2006, 118, 8415; Angew. Chem. Int. Ed. 2006, 45, 8235; f) C.
Gonzꢃlez-Arellano, A. Abad, A. Corma, H. Garcꢄa, M. Iglesias,
F. Sꢃnchez, K. Kaneda, Angew. Chem. 2007, 119, 1558; Angew.
Chem. Int. Ed. 2007, 46, 1536; g) T. Mitsudome, K. Nose, K.
Mori, T. Mizugaki, K. Ebitani, K. Jitsukawa, Angew. Chem. 2007,
119, 3352; Angew. Chem. Int. Ed. 2007, 46, 3288; h) K.
Yamaguchi, H. Fujiwara, Y. Ogasawara, M. Kotani, N. Mizuno,
K. Jitsukawa, K. Kaneda, Angew. Chem. 2007, 119, 3996; Angew.
Chem. Int. Ed. 2007, 46, 3922.
Baiker, J. Am. Chem. Soc. 2007, 129, 10582.
[19] a) T. Thorpe, J. Blacker, S. M. Brown, C. Bubert, J. Crosby, S.
Fitzjohn, J. P. Muxworthy, J. M. J. Williams, Tetrahedron Lett.
2001, 42, 4041; b) Y. Y. Li, H. Zhang, J. S. Chen, X. L. Liao, Z. R.
Dong, J. X. Gao, J. Mol. Catal. A 2004, 218, 153; c) J. S. Chen,
Y. Y. Li, Z. R. Dong, B. Z. Li, J. X. Gao, Tetrahedron Lett. 2004,
45, 8415; d) B. Z. Li, J. S. Chen, Z. R. Dong, Y. Y. Li, Q. B. Li,
J. X. Gao, J. Mol. Catal. A 2006, 258, 113; e) X. Q. Zhang, Y. Y.
Li, H. Zhang, J. X. Gao, Tetrahedron: Asymmetry 2007, 18, 2049;
f) G. Chen, Y. Xing, H. Zhang, J. X. Gao, J. Mol. Catal. A 2007,
273, 284; g) W. He, B. L. Zhang, R. Jiang, P. Liu, X. L. Sun, S. Y.
Zhang, Tetrahedron Lett. 2006, 47, 5367.
[20] a) C. Maillet, P. Janvier, M. Pipelier, T. Praveen, Y. Andres, B.
Bujoli, Chem. Mater. 2001, 13, 2879; b) C. A. Jaska, I. Manners, J.
Am. Chem. Soc. 2004, 126, 9776; c) S. Ikeda, S. Ishino, T. Harada,
N. Okamoto, T. Sakata, H. Mori, S. Kuwabata, T. Torimoto, M.
Matsumura, Angew. Chem. 2006, 118, 7221; Angew. Chem. Int.
[21] a) G. M. Whitesides, M. Hackett, R. L. Brainard, J. P. P. M.
Lavalleye, A. F. Sowinski, A. N. Izumi, S. S. Moore, D. W.
Brown, E. M. Staudt, Organometallics 1985, 4, 1819; b) J. A.
Widegren, M. A. Bennett, R. G. Finke, J. Am. Chem. Soc. 2003,
125, 10301; c) J. A. Widegren, R. G. Finke, J. Mol. Catal. A 2003,
198, 317; d) Y. Lin, R. G. Finke, Inorg. Chem. 1994, 33, 4891.
9244 www.angewandte.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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