A simple and highly effective method for hydrogenation of arenes by [Rh(COD)Cl]2

Article abstract of DOI:10.1016/j.tetlet.2008.12.108

Hydrogenation of arenes, including chiral BINOLs and the lignin model compounds, has been achieved efficiently by using the simple complex [Rh(COD)Cl]₂ as catalyst precursor.

Full text of DOI:10.1016/j.tetlet.2008.12.108

Tetrahedron Letters 50 (2009) 1282–1285
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Tetrahedron Letters
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A simple and highly effective method for hydrogenation of arenes
by [Rh(COD)Cl]2
a
a
a,b,*
Da-Wei Wang , Sheng-Mei Lu , Yong-Gui Zhou
a
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, China
State Key Laboratory of Organometallic Chemsitry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Hydrogenation of arenes, including chiral BINOLs and the lignin model compounds, has been achieved
Received 27 October 2008
Revised 19 December 2008
Accepted 23 December 2008
Available online 8 January 2009
efficiently by using the simple complex [Rh(COD)Cl]
2
as catalyst precursor.
Ó 2009 Elsevier Ltd. All rights reserved.
The complete hydrogenation of arenes to non-aromatic cyclic
compounds and that of phenols to alcohols represent important
industrial catalytic transformation due to the increasing industrial
demand for low aromatic diesel fuels.1 Moreover, the hydrogena-
tion of benzene to cyclohexane, which has been used primarily
in the production of adipic acid, a precursor to nylon, is probably
the most important industrially practiced arene hydrogenation
the selectivity is moderate. Low reactivity were obtained in THF,
EtOAc, and EtOH, good reactivity with moderate selectivity was ob-
tained in MeOH, and high reactivity and selectivity of compound
2a were obtained in i-PrOH (Table 1, entry 6). Excitingly, we found
that the reactions performed in air revealed high catalytic activity
than those in nitrogen (Table 1, entries 6 and 7). The results re-
vealed that the hydrogenation was oxygen promoted by using this
2
11
reaction. In most cases, arene hydrogenation has been performed
method. Subsequently, when the catalyst loading was reduced to
with heterogeneous catalysts such as Rh/C, Rh/Al
2
O
3
, Pd/C and Ra-
0.01 mol %, only 33% of conversion was obtained. Next, some com-
mercially available stabilizers were also investigated for the hydro-
genation of phenol. The results were summarized in Table 1 and
4 Å MS gave the best result.
3
ney nickel or others under drastic reaction conditions. Recently,
Roucoux et al. and Xu et al. have developed the liquid–liquid bi-
phasic conditions for arene hydrogenation.4 Finke et al. used the
metal nanoparticles as catalysts for the hydrogenation of arenes
2
In the presence of 0.25 mol % of [Rh(COD)Cl] and 50 mg of 4 Å
5
and ketones. Park and coworkers reported rhodium and iridium
MS, a variety of substituted phenols have been tested to examine
the reaction scope (Table 2). The hydrogenation of phenol was
completed, and cyclohexanol was the sole product (Table 2, entry
1). The substituted monocyclic phenols were hydrogenated
smoothly with excellent reactivities and selectivities to give the
substituted cyclohexanols (Table 2, entries 2–6). However, the
hydrogenation of 2-hydroxybiphenyl was not complete under the
standard conditions, which might be attributed to steric effect.
When the catalyst loading was enhanced to 0.50 mol %, full conver-
sion and 95% selectivity were obtained (Table 2, entry 3). This
hydrogenation system could tolerate a big t-butyl group, and gave
high yield of 4-t-butyl cyclohexanol, which was an useful interme-
diate in the fragrance and perfume industries (Table 2, entry 6).
We also conducted the hydrogenation of benzene and some of
its classical derivatives under optimal conditions (Table 3). The
results showed that the hydrogenation was complete (Table 3,
entries 1–4). For the heteroaromatic compounds such as 2-methyl-
furan, good reactivity and selectivity of 4e could also be obtained.
Similar results were also obtained in the hydrogenation of 3f and
3g (Table 3, entries 6 and 7). Two products were obtained (72%
of 4h and 28% of 4i) in the hydrogenation of benzalacetone. For
methyl 4-hydrobenzoate, 4j was obtained as the desired and
sole product. From these results, it might be inferred that this
6
nanoparticles as the catalysts for the hydrogenation of arenes.
Other conditions for arene hydrogenation were also developed,
conditions,7 ionic liquid condition, and
8
such as supercritical CO
others.
2
9
Recently, we developed a method for the highly enantioselec-
tive hydrogenation of quinoline derivatives using chiral iridium
1
0
complexes. As a test case, we attempted the hydrogenation of
substituted phenols, but the almost racemic products were ob-
tained in all tried conditions using chiral rhodium or ruthenium
complexes as catalysts. Further studies found that the hydrogena-
2
tion reaction can still occur in air using the [Rh(COD)Cl] as catalyst
in the absence of chiral ligands and bases. In this Letter, we re-
ported the hydrogenation of arenes, including phenols, especially
enantiopure BINOL in air using [Rh(COD)Cl]2.
In our initial investigation, we found that the [Rh(COD)Cl]
2
could catalyze the hydrogenation of phenol in air with moderate
activity. In order to obtain high selectivity of the main product,
the effect of solvents was evaluated (Table 1). This reaction was
2 2
strongly solvent dependent. For CH Cl , the reactivity is high, and
*
Corresponding author. Tel./fax: +86 411 84379220.
E-mail address: ygzhou@dicp.ac.cn (Y.-G. Zhou).
0
040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.12.108

D.-W. Wang et al. / Tetrahedron Letters 50 (2009) 1282–1285
1283
Table 1
Optimization of the reaction conditions for the hydrogenation of phenol
Table 3
a
a
Hydrogenation of benzene derivatives and others
[
Rh(COD)Cl]
2
/H
2
(50 atm)
Selectivity (%) b
Entry
1
Substrate
Product
OH
OH
+
O
Air / RT /
i-PrOH
2a1
97 (4a)
1
a
2a
1
Entry
Solvent
THF
Stabilizer
Convn.(%)c
2a(%)
2a (%)
2
3
4
5
6
96 (4b)
92 (4c)
99 (4d)
1
2
3
4
5
6
7
8
9
None
None
None
None
None
None
None
None
4 Å MS
24
97
36
93
45
>99
12
35
19
62
22
98
22
17
99
62
46
27
18
12
56
17
26
20
0
2 2
CH Cl
OMe
OMe
Et
EtOAc
MeOH
EtOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
i-PrOH
d
52
24
6
b
93 (4e)
33
O
O
O
b
>99
0
b
O
OH
O
10
11
12
13
Al
2
O
3
87
25
20
26
14
>95 (4f)c
b
Aliquat 336
PVP
TBAB
66
56
OEt
OEt
O
b
b
O
32
>95 (4g)c
7
8
Ph
OMe
Me
Cy
OMe
a
Conditions: 10 mmol substrate, [Rh(COD)Cl]
0 mL solvent, 50 atm H , H /air = 50:1, rt, 14–16 h.
5 mmol substrate, [Rh(COD)Cl] (1.3 mg, 0.0025 mol, 0.01 mol %), 20 mL
solvent.
2
(1.3 mg, 0.0025 mol, 0.025 mol %),
O
O
1
2
2
72 (4h)c
b
2
2
Ph
Cy
Me
c
Determined by GC analysis of the crude product.
The reaction was carried out in N .
2
OH
Me
d
28 (4i)c
Cy
9
HO
CO Me
>95 (4j)c
92 (4k)
HO
CO Me
2
2
Table 2
a
Hydrogenation of phenol derivatives
1
4
0
[
Rh(COD)Cl]
2
(0.25 mol%)
-PrOH
OH
+
H
2
(50 atm)
o
OH
a
Conditions: 1 mmol substrate, [Rh(COD)Cl]2 (0.25 mol %), 6 mL i-PrOH, 50 mg
, H /air = 50:1, rt, 14–16 h.
Determined by GC analysis of the crude product, 100% convn.
Determined by 1H NMR analysis of the crude product.
R
R
4
A MS / Air / RT /
i
Å MS, 50 atm H
2
2
1
2
b
c
Entry
Substrate
OH
OH
Selectivity (%)b
cis/trans c
Product
1
2
99 (2a)
—
OH
OH
styrene gave a mixture of 4d (72%) and 4l (28%), which suggested
that the hydrogenation of alkenes is easier than that of benzene
ring (Table 4, entry 5).
At the same time, phenol was hydrogenated in a gram scale at
room temperature (Table 5). We performed the reaction of 2.5 g
97 (2b)
82:18
81:19
OH
Ph
OH
Cy
95 (2c) d
of phenol with [Rh(COD)Cl]
. 2a was found as the sole product with full conversion, and
the TON was up to 10,640 (Table 5, entry 4). When we added the
substrate up to 5.0 g with the same quantity of [Rh(COD)Cl]
0.005 mol %, 1.3 mg) under 50 atm of H , 84% of 2a and 16% of
2
(0.01 mol %, 1.3 mg) under 50 atm of
3
H
2
4
5
6
Ph
OH
99 (2d)
92 (2e)
92 (2f)
69:31
81:19
63:37
Cy
OH
2
(
2
cyclohexanone with 97% conversion were determined by GC anal-
ysis, and the TON was up to 20,642 (Table 5, entry 5). Importantly,
the catalyst in situ from the complex [Rh(COD)Cl] showed much
2
MeO
t-Bu
OH
OH
MeO
t-Bu
OH
OH
higher reactivity than the commercial Rh/C as a catalyst in the
a
hydrogenation reaction (Table 5, entries 4 and 6).
Conditions: 1 mmol substrate, [Rh(COD)Cl]
Å MS, 50 atm H , H /air = 50:1, rt, 14–16 h.
2
(0.25 mol %), 6 mL i-PrOH, 50 mg
0
4
2
2
Optically active H
8
-1,1 -bi-2-naphthol (H
8
-BINOL) is a very use-
b
12
Determined by GC analysis of the crude product, 100% convn.
ful starting material for the synthesis of relevant chiral ligands.
However, the literature about the synthesis of their derivatives is
c
Determined by 1H NMR analysis of the crude product.
d
[
2
Rh(COD)Cl] (0.5 mol %) was used.
1
3
rare. Gram et al. reported a widely used method for the synthesis
of H -BINOL using PtO as a catalyst; however, the catalyst is very
8
2
13a
hydrogenation system is more effective for the hydrogenation of
alkenes and arenes than that of ketones. It is well known that
the hydrogenation of higher olefins is far less effective. Here, this
system was successfully used in the hydrogenation of 1-octene
expensive and the reaction time was too long (7 days). Sugimura
developed the hydrogenation of BINOL using Pd/C as a catalyst, and
1
3b
the yield was somewhat low (70%).
Ding et al. reported the
reduction of chiral BINOL using Raney Ni/Al alloy with 97% ee of
1
3c
(
Table 3, entry 10).
product. Recently, Korostylev et al. developed the hydrogenation
1
3d
To show the effectiveness of the catalyst further, we studied the
of BINOL using Pd/C and Ru/C as catalysts.
Motoyama et al. re-
hydrogenation of some arenes under solvent-free conditions. Ben-
zene was hydrogenated using [Rh(COD)Cl] (0.05 mol %) in full
conversion, and 4a was obtained as the sole product (Table 4, entry
). Toluene and anisole were also completely converted to the cor-
responding 4b and 4c, respectively. Importantly, the hydrogena-
tion of 2-methylfuran and 1-octene was also complete with high
selectivities; 4e and 4k were found as the sole products. However,
ported the hydrogenation of BINOLs using carbon nanofiber-sup-
1
3e
2
ported ruthenium nanoparticles as catalysts.
new and efficient method for hydrogenation of BINOL using
[Rh(COD)Cl] in i-PrOH.
The hydrogenation of binaphthols was carried out with
[Rh(COD)Cl] in i-PrOH at 80 °C under 50 atm of H pressure
(Table 6). Under these conditions, the reaction proceeds well, and
Here, we report a
1
2
2
2

1
284
D.-W. Wang et al. / Tetrahedron Letters 50 (2009) 1282–1285
Table 4
2
of BINOL with 0.1 mol % of [Rh(COD)Cl] (80 °C, 50 atm of H2, in
air). Full conversion was achieved, and optically pure 6a was
obtained.
For the above catalytic system for hydrogenation of arenes
2
using the simple complex [Rh(COD)Cl] , the active catalytic species
a
Hydrogenation of various arenes at room temperature without solvent
Entry
1
Substrate
Convn.(%)b
Product
>95 (4a)
may be rhodium nanoparticles or heterogeneous rhodium cata-
lysts. It is well known that mercury is a good and accepted heter-
ogeneous catalyst poison, due to its classical adsorption onto the
2
3
>95 (4b)
>95 (4c)
OMe
OMe
4
b,5a
catalyst surface.
Therefore, the behavior of the catalytic system
was tested by using this method. Subsequently, phenol was se-
lected as the reference substrate in the mercury poisoning experi-
ment. A dark reaction solution, which was obtained from the
4
5
>95 (4e)
28 (4d)
O
O
Et
Et
2
complex [Rh(COD)Cl] , was stopped after about 50% conversion,
7
2 (4l)
and 300 equiv of mercury was added. After stirring for 1 h, the
solution was reconnected to stainless steel autoclave, and the
hydrogen was charged again. No further loss of phenol was de-
tected, this result showed that Hg had completely poisoned the
catalyst (see Supplementary data), which offer some evidences
that rhodium(0) nanoparticles may be the catalytic active species.
In our catalytic system, air or oxygen is crucial for the reactivity
and selectivity. Recently, Liu reported the oxygen-promoted Suzuki
coupling reaction by the in situ-generated palladium nanoparticles
6
>95 (4k)
a
Conditions: 20 mmol substrate, [Rh(COD)Cl]
, H /air = 50:1, rt, 14–16 h.
Determined by 1H NMR analysis of the crude product.
2
(0.05 mol %), 100 mg 4 Å MS,
5
0 atm H
2
2
b
Table 5
a
Hydrogenation of phenol in a gram scale
1
4
[
Rh(COD)Cl]
2
/
i
-PrOH
under aerobic condition. The report prompted us to suppose that
the catalysts may be rhodium nanoparticles generated from the
OH
+
H
2
(50 atm)
OH
o
4
A MS / Air / RT
2
complex [Rh(COD)Cl] in situ under aerobic condition in our reac-
1
a
2a
tion. As a result, the oxygen-promoted rhodium nanoparticles
might be formed easily and maintained high catalytic activity
(see Supplementary data).
In summary, we have developed a simple, highly effective
hydrogenation of arenes, which provide direct access to saturated
8
cyclic compounds. Furthermore, enantiopure H -BINOL derivatives
could also be obtained easily by using this method. Further inves-
tigation on the mechanism and the range of substrates is currently
in progress.
Entry
Substrate (g)
Cat. (mol %)
Convn./2a(%)b
TON
2
c,f,14
0.1c
1
2
3
4
5
6
1.0
1.0
1.0
2.5
5.0
2.5
99/98
99/99
99/99
99/99
1064
2128
4256
10,640
20,642
4788
0.05d
0.02
0.01
e
0.005
97/84
f
g
0.02
90/67
a
Conditions: [Rh(COD)Cl]
, H /air = 50:1, rt, 14–16 h.
Determined by GC analysis of the crude product.
2
(1.3 mg, 0.0025 mmol), i-PrOH, 100 mg 4 Å MS,
5
0 atm H
2
2
b
c
d
e
f
[
[
Rh(COD)Cl]
Rh(COD)Cl]
2
(5.2 mg) was used.
(2.6 mg) was used.
Acknowledgments
2
16% of cyclohexanone was detected.
Rh/C (20.6 mg, 0.0050 mmol) was used as a catalyst.
We are grateful for the financial support from National Science
Foundation of China (20532050 and 20621063) and Chinese acad-
emy of Sciences.
g
3
3% of cyclohexanone was detected.
Table 6
Supplementary data
a
Hydrogenation of BINOL derivatives
R1
R3
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2008.12.108.
OR2
OR2
[Rh(COD)Cl]
2
/ H ( 50 atm)
OR2
OR2
2
o
-PrOH / 4A MS / 80 oC / Air
References and notes
i
R1
R3
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2
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2
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/air = 50:1, rt, 14–16 h.
b
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