Table 1 Hydrogenation of benzene and anisole with various catalysts
a
Yield (%)
b
c
Catalyst
Substrate
Solvent
T/uC
pH
2
/atm
t/h
0.5
6
2
S/C
TOF
1
2
3
4
5
6
7
8
9
1
1
1
a
1
1
Benzene
Benzene
Benzene
Benzene
Anisole
Anisole
Anisole
Anisole
Anisole
Anisole
Anisole
Anisole
Hexane
Solventless
Solventless
22
75
75
30
22
75
75
22
22
20
40
22
1
4
4
7
1
4
4
1
1
1
1
3
100
100
100
100
100
100
100
10000
250
2000
100
10000
250
100
100
100
600
5000
375(657)
750
d
Ir
Rh/PVP
e
f
H
2
O
Hexane
8
1
1
1
Ir
300
Solventless
Solventless
Hexane
30
18
1
1
3.6
1000
30(54)
12
d
g
62
h
i
Rh/Al
Rh/Al
2
O
O
3
4
0
100
42
91
2
3
Hexane
0
84
j
f
0
1
2
Rh/HEAC16Br
Rh-Pd /SiO
Rh/TBA-POA
H
2
O
Heptane
k
2
9
144
2810
2600
393
54
l
m
PC
b
Determined by GC. Substrate/catalyst. Turnover frequency defined as mol of H
PVP 5 poly(N-vinyl-2-pyrrolidone).
Biphasic system. Cyclohexane was also produced in 16% yield at 74% conversion. Dugussa type purchased from Aldrich. Purchased from
c
d
consumed per mol of total metal per hour. In
2
4
e
14
parenthesis TOF corrected for the exposed atoms of iridium nanoparticles. Iridium nanoparticles.
f
g
h
i
j
Acros. HEAC16Br 5 N,N-dimethyl-N-(2-hydroxyethyl)ammonium bromide.
3
k
l
Ref. 5. TBA-POA 5 tetrabutylammonium polyoxoaninon.
7
m
PC 5 propylene carbonate.
and a commercial Rh/Al
aluminum nuclei surrounded by oxygens in octahedral structure.
The resonance at 60 ppm is also observed in the spectrum of
2
O
3
, which is corresponding to the
frequency (TOF) reached 5000 under 4 atm H at 75 uC and
was 13 times higher than that given by the iridium catalyst. The
2
11
high activity of 1 was also shown in the hydrogenation of anisole 1;
it is the highest among the commercially available Rh catalysts and
the reported ones. Notably, 1 can be recovered simply by filtration
and reused ten times without activity loss.
12
2 3
Rh/Al O , which reflects a tetrahedral structure. A trigonal-
bipyramidal structure or Al–O–Rh bonds would be responsible for
1
3
the unique resonance at 35 ppm. BET nitrogen adsorption
analysis reveals that the BET surface area, the pore volume and
21
The scope of arene hydrogenation with 1 was investigated with
2
21
3
the pore size of 1 are 616 m g , 0.85 cm g and 2.9 nm,
respectively.
various arenes at room temperature under 1 atm H (Table 2). Our
2
catalyst 1 was active for monosubstituted arenes such as toluene,
phenol, ethyl benzoate and 1-phenylethanol. Interestingly, the
hydrogenation of acetophenone produced 1-cyclohexylethanol as
the major product in 65% yield while cyclohexylmethyl ketone was
intact under the same conditions. Disubstituted arenes were also
hydrogenated successfully with stereoselectivities between 94:6 to
52:48. Naphthalene was hydrogenated selectively to tetralin or
decalin by controlling reaction time. Likewise, quinoline was
hydrogenated selectively to give tetrahydroquinoline in high yield.
In conclusion, we have developed a simple synthetic method for
a new rhodium catalyst that is recyclable and highly active in the
hydrogenation of various arenes under mild conditions. The highly
porous and fibrous matrix and the proper size of rhodium particles
in our catalyst should be factors for the observed high activity. We
are investigating the detailed effect of metal particle size and the
role of hydroxy groups of the matrix on catalytic activity.
This work was supported by the Korea Research Foundation
Grant (KRF-2004-005-C00007).
We tested the activity of 1 in the hydrogenation of benzene and
anisole and compared the activity with those of commercially
available rhodium catalysts and also with those reported
previously (Table 1). Benzene was hydrogenated to cyclohexane
completely within 30 min at 22 uC under 1 atm H
1 mol% Rh). This activity is similar to that of a polymer-stabilized
rhodium catalyst (Rh/PVP) under the conditions of 7 atm H and
2
by using 1
(
2
1
4
3
0 uC. The activity of 1 was much higher than that of an iridium
4
catalyst known for solventless hydrogenation; the turnover
Table 2 Hydrogenations of arenes at room temperature under 1 atm
a
H
2
b
t/h Yield (%) cis:trans TOF
c
Entry Substrate
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
a
Toluene
Phenol
Ethyl benzoate
1-Phenylethanol
Acetophenone
p-Xylene
m-Xylene
o-Xylene
p-Cresol
1
1
100
100
300
300
67
4.5 100
100
4
75
67
d
4.5 35
1.5 100
2.3 100
2.5 100
3 100
3.5 100
72:28
82:18
94:6
60:40
52:48
52:48
85:15
200
130
120
100
86
100
1.3
65
Notes and references
1
In Nanoparticles: From Theory to Application, ed. G. Schmid, Wiley-
VCH, Weinheim, 2004; F. Raimondi, G. G. Scherer, R. K o¨ tz and
A. Wokaun, Angew. Chem., Int. Ed., 2005, 44, 2190.
0
1
2
3
4
5
m-Cresol
o-Cresol
3
Dimethyl terephthalate 46
100
100
97
e
f
2 A. Roucoux, J. Schulz and H. Patin, Chem. Rev., 2002, 102, 3757;
J. M. Thomas, B. F. G. Johnson, R. Raja, G. Sankar and P. A. Midgley,
Acc. Chem. Res., 2003, 36, 20; P. J. Dyson, Dalton Trans., 2003, 2964;
J. A. Widegren and R. G. Finke, J. Mol. Catal. A: Chem., 2003, 191,
187; J. A. Widegren and R. G. Finke, J. Mol. Catal. A: Chem., 2003,
198, 317.
g
h
Naphthalene
Naphthalene
Quinoline
3
10
6
100
94
88:12
50
9
f
At 22 uC, 0.50 mmol of substrate in hexane (1.0 mL) was reacted
b
c
with 1 (1 mol% Rh). Determined by GC. Turnover frequency
defined as mol of H consumed per mol of total metal per hour.
Based on the yields of cyclohexylmethyl ketone and
3
J. Schulz, A. Roucoux and H. Patin, Chem. Commun., 1999, 535;
A. Roucoux, J. Schulz and H. Patin, Adv. Synth. Catal., 2003, 345, 222;
V. M e´ vellec, A. Roucoux, E. Ramirez, K. Philippot and B. Chaudret,
Adv. Synth. Catal., 2004, 346, 72.
2
d
e
f
1-cyclohexylethanol. Ethyl acetate (2 mL) was used. 5 mol% of
Rh was used. Tetralin was the major product and decalin was
g
h
produced in 3%. Decalin was produced exclusively.
4 C. J. Boxwell, P. J. Dyson, D. J. Ellis and T. Welton, J. Am. Chem. Soc.,
002, 124, 9334; G. S. Fonseca, A. P. Umpierre, P. F. P. Fichtner,
2
5
668 | Chem. Commun., 2005, 5667–5669
This journal is ß The Royal Society of Chemistry 2005