A rhodium-grafted hydrotalcite as a highly efficient heterogeneous catalyst for 1,4-addition of organoboron reagents to α,β-unsaturated carbonyl compounds

Article abstract of DOI:10.1016/j.tetlet.2006.05.075

Treatment of a hydrotalcite with an aqueous solution of rhodium trichloride results in a Rh-grafted hydrotalcite (Rh/HT) with monomeric Rh species on the surface, which successfully promoted 1,4-addition of organoboron reagents to α,β-unsaturated carbonyl compounds. Furthermore, this catalyst was reusable and was found to be applicable to a one-pot synthesis of 3,3-diarylnitrile.

Full text of DOI:10.1016/j.tetlet.2006.05.075

Tetrahedron Letters 47 (2006) 5083–5087
A rhodium-grafted hydrotalcite as a highly efficient
heterogeneous catalyst for 1,4-addition of organoboron
reagents to a,b-unsaturated carbonyl compounds
a
a
b
a
Noriaki Fujita, Ken Motokura, Kohsuke Mori, Tomoo Mizugaki,
a
c
a,
*
Kohki Ebitani, Koichiro Jitsukawa and Kiyotomi Kaneda
a
Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University,
-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan
Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University,
-2 Yamadaoka, Suita, Osaka 565-8071, Japan
1
b
1
c
Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology,
Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan
Received 5 April 2006; revised 9 May 2006; accepted 15 May 2006
Available online 6 June 2006
Abstract—Treatment of a hydrotalcite with an aqueous solution of rhodium trichloride results in a Rh-grafted hydrotalcite (Rh/HT)
with monomeric Rh species on the surface, which successfully promoted 1,4-addition of organoboron reagents to a,b-unsaturated
carbonyl compounds. Furthermore, this catalyst was reusable and was found to be applicable to a one-pot synthesis of 3,3-
diarylnitrile.
ꢀ
2006 Elsevier Ltd. All rights reserved.
Nanostructured heterogeneous catalysts with stable and
well defined surface active sites, are currently receiving
considerable attention, because their unique properties
carbon bonds. In 1997, Miyaura et al. reported a Rh-
catalyzed 1,4-addition reaction of organoboron reagents
to a,b-unsaturated carbonyl compounds. The discovery
6
1
such as reusability and ease of handling and separation,
of this new reaction triggered much research activity in
provide a means of addressing environmental and
economic concerns. Hydrotalcites (HTs), which possess
cation and anion exchange abilities, as well as strong
surface basicity and adsorption capacity, are promising
inorganic materials for the development of high-perfor-
the area of Rh-catalyzed carbon–carbon bond forma-
7
–9
tion.
However, the homogeneous catalytic systems
thus far developed often suffer from disadvantages such
as requirements for toxic and expensive phosphine li-
gands, low catalytic activities, and tedious work-up pro-
2
–4
10
mance heterogeneous catalysts. We recently reported
new strategies for the design of solid catalysts, utilizing
modified hydrotalcites for various organic reactions,
such as epoxidation of olefins using hydrogen perox-
cedures. In this paper, we describe a rhodium-grafted
hydrotalcite catalyst (Rh/HT) for highly efficient hetero-
geneous 1,4-addition of organoboronic acids to a,b-
unsaturated carbonyl compounds (Scheme 1).
5
a,b
5c,d
ide,
oxidation of alcohols,
and carbon–carbon
5
e–h
Preparation of the Rh/HT is as follows: the HT11
bond formation, including one-pot syntheses.
(1.0 g), was added to 100 mL of an aqueous solution
Since carbon–carbon bond formation is one of the most
important reactions in the synthetic organic chemistry,
new catalytic methods are continually developed,
employing not only acids and bases, but also transition
metals, for efficient formation of a variety of carbon–
R1
R2
B(OH)2
Rh/HT
X
+
X
R2
O
R1
O
*
Corresponding author. Tel./fax: +81 6 6850 6260; e-mail: kaneda@
cheng.es.osaka-u.ac.jp
Scheme 1. 1,4-Addition of arylboronic acids to a,b-unsaturated
carbonyl compounds using the Rh/HT catalyst.
0040-4039/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.05.075

5084
N. Fujita et al. / Tetrahedron Letters 47 (2006) 5083–5087
a
Table 1. 1,4-Addition of phenylboronic acid to 2-cyclohexene-l-one
then, washed thoroughly with deionized water, and
dried under vacuum at room temperature, affording
Rh/HT as a pink powder (Rh content: 2.0 wt %). The
Rh/HT was characterized by X-ray diffraction (XRD),
and X-ray absorption fine structure (XAFS). The
XRD peak positions of the Rh/HT were identical to
those of the parent HT. The Rh K-edge XANES spec-
trum of the Rh/HT was similar to that of RhCl ÆnH O.
Rh catalyst (Rh: 1.2 mol%)
O
O
1
,5-cod (1.0 eq. of Rh)
+
PhB(OH)2
solvent, 100 ºC, Ar
Ph
1
2
3
Entry
1
Catalyst
Solvent
Yield (%)
3
2
3
In Fourier transformation (FT) of k -weighted Rh K-
Rh/HT
Rh/HT
Rh/HT
Rh/HT
Rh/HT
Rh/HT
Rh/HT
Rh/HT
Rh/HT
Rh/MgO
1,4-Dioxane
1,4-Dioxane
Ethanol
DME
Toluene
DMF
n-Heptane
THF
98
2
˚
b
edge EXAFS, the lack of peaks around 2.0–3.0 A
2
showed that there were no Rh–Rh or Rh–O–Rh bonds
in the Rh/HT. From these results, monomeric Rh(III)
species is grafted on the HT surface.
3
4
5
6
7
8
9
98
97
36
33
28
26
0
55
20
Trace
0
The catalytic activity of the Rh/HT for the 1,4-addition
reaction of phenylboronic acid (2) to 2-cyclohexen-1-one
Water
(
1) was compared with those of various solid-supported
10
11
12
13
14
15
16
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
Rh catalysts (Table 1). The Rh/HT combined with 1,5-
cyclooctadiene (1,5-cod) exhibited the highest catalytic
activity, giving 3-phenyl-cyclohexanone (3) in 98% yield
Rh/Mg(OH)
Rh/Al
Rh/Al(OH)
2
2
O
3
3
(
entry 1), while the reaction occurred only to a slight ex-
3
RhCl ÆH
HT
2
O
0
0
0
c
12
tent in the absence of 1,5-cod (entry 2). Other hetero-
geneous Rh catalysts, such as Rh/MgO, Rh/Mg(OH)2,
Rh/Al O , and Rh/Al(OH) were found to be less active
None
a
2
3
3
Reaction conditions: Rh catalyst (Rh; 0.012 mmol), 1,5-cycloocta-
diene (0.012 mmol), 2-cyclohexene-l-one (1.0 mmol), phenyl boronic
acid (1.0 mmol), solvent (2.0 mL), 100 ꢁC, Ar, 4 h.
Without l,5-cyclooctadiene.
(
entries 10–13). Neither the RhCl ÆnH O precursor
3 2
(entry 14) nor the parent HT (entry 15) gave any
b
c
1,4-addition products. In the Rh/HT-catalyzed reaction,
1,4-dioxane, ethanol, and dimethoxy ethane (DME)
were found to be good solvents, affording 98%, 98%,
and 97 % yields of the corresponding 1,4-adduct,
respectively (entries 1, 3, and 4). In contrast, THF, tol-
uene, n-heptane, and DMF were poor solvents (entries
5–8), and no reaction was observed in water (entry 9).
HT (0.06 g) was used.
À3
of RhCl ÆnH O (Rh; 2.0 · 10 M), and the hetero-
geneous mixture was stirred at room temperature for
.5 h. The solid product was separated by filtration,
3
2
0
a
Table 2. 1,4-Addition of organoboron reagents to a,b-unsaturated carbonyl compounds using the Rh/HT catalyst
b
Entry
Acceptor
Donor
Product
Temperature (ꢁC)
Time (h)
4
Yield (%)
O
1
1
2
100
92
75
Ph
O
O
c
2
2
150
5
Ph
Ph
3
2
2
100
150
4
8
92
76
O
O
O
O
Ph
c,d
4
O
O
Ph
c,d
5
2
2
2
150
150
150
24
4
99
Ph
Ph
Ph
Ph
Ph
Ph
Ph
e
6
7
Ph
CHO
74
CHO
CN
e
CN
8
61
Ph
Ph
O
O
O
O
e
8
2
100
4
61
Ph

N. Fujita et al. / Tetrahedron Letters 47 (2006) 5083–5087
5085
Table 2 (continued)
b
Entry
Acceptor
Donor
Product
Temperature (ꢁC)
Time (h)
Yield (%)
O
B(OH)2
9
1
1
100
100
4
99
O
O
B(OH)2
1
1
0
1
4
4
75
78
MeO
Cl
OMe
Cl
B(OH)2
1
100
a
Reaction conditions: Rh/HT (0.06 g; Rh: 0.012 mmol), 1,5-cyclooctadiene (0.012 mmol), acceptor (1.0 mmol), organoboron reagent (l.0 mmol),
,4-dioxane (2.0 mL), 100 ꢁC, Ar, 4 h.
1
b
c
Isolated yield based on acceptor.
.5 equiv of organoboron reagent were used.
1
d
e
Rh/HT (0.12 g; Rh: 0.024 mmol).
GC yield.
Table 2 presents a summary of 1,4-addition reaction of
arylboronic acids to a,b-unsaturated carbonyl com-
pounds in the presence of the Rh/HT catalyst and
reaction of 2 to 1 using 0.05 mol % of the Rh/HT affor-
1
4
ded 3 in 81% isolated yield with a high TON of 1620
À1
and TOF of 135 h : these values are considerably
1
,4-dioxane solvent. Both aliphatic and aromatic enones
higher than those previously reported for homogeneous
À1 7,15
were found to be good acceptors (entries 1–5); for exam-
ple, methyl vinyl ketone readily reacted with 2 to give 4-
phenyl-2-butanone in 92% isolated yield (entry 3). The
Rh/HT catalyst system was found to be applicable to
an a,b-unsaturated aldehyde and nitrile (entries 6 and
reaction systems (TON; 1–100, TOF; 1–33 h
(Scheme 2).
)
The spent Rh/HT catalyst was easily separated from the
reaction mixture by simple filtration. The recovered cat-
alyst was found to be reusable with retention of its high
catalytic activity and selectivity; yields of over 90% were
attained for at least the two catalyst-recycling reactions
7
): cinnamaldehyde reacted with 2 to give 3,3-diphenyl
propanal, an important intermediate in the synthesis
1
3
of quinoline synthesis, without the formation of the
,2-addition product (entry 6). Electron variation of p-
1
6
1
of 1 and 2. ICP analysis of the filtrate showed 2%
leaching of Rh species during the above reactions, how-
ever, the filtrate was found not to promote the addition
reaction.
substituted phenylboronic acids did not strongly affect
product yields (entries 1, 9–11). A large-scale addition
Rh/HT (Rh: 0.05 mol%)
O
O
A XANES spectrum of the used Rh/HT catalyst showed
retention of +3 oxidation state of the Rh species on
the HT. Based on the reaction mechanism reported
1
,5-cod (1.0 eq. of Rh)
+
PhB(OH)2
1
,4-Dioxane, 100 ºC, Ar, 12 h
7
b
Ph
for homogeneous Rh catalysts, the Rh/HT-catalyzed
reaction may involve the transmetalation between the
Yield: 81%
TON: 1620
TOF: 135 h-1
17
rhodium hydroxide and arylboronic acid to give an
arylrhodium species, followed by insertion of the enone.
The rhodium enolate may then undergo hydrolysis to
give the 1,4-addition product and a rhodium hydroxide
species. Because formation of Rh clusters was observed
during the reaction in the absence of 1,5-cod, it is
Scheme 2. Large scale 1,4-addition of phenylboronic acid to
-cyclohexen-1-one catalyzed by the Rh/HT.
2
Ph
Base Sites
CO Et
2
Rh Species
PhB(OH)2
CO2Et
CN
NC
CO Et
+
Ph
O
Ph
2
Ph
CN
Overall yield; 74%
Scheme 3. Three-component reaction using the Rh/HT catalyst.

5086
N. Fujita et al. / Tetrahedron Letters 47 (2006) 5083–5087
thought that 1,5-cod acts as a ligand for the surface Rh
Commun. 1998, 1033; (b) Abell o´ , S.; Medina, F.; Tichit,
D.; P e´ rez-Ram ´ı rez, J.; Groen, J. C.; Sueiras, J. E.; Salagre,
P.; Cesteros, Y. Chem. Eur. J. 2005, 11, 728.
. Our work; Epoxidation: (a) Yamaguchi, K.; Mori, K.;
Mizugaki, T.; Ebitani, K.; Kaneda, K. J. Org. Chem. 2000,
1
8
species, preventing aggregation. However, studies on
the mechanistic details and the structure of the Rh spe-
cies are in progress.
5
6
5, 6897; (b) Honma, T.; Nakajo, M.; Mizugaki, T.;
The potential versatility of the Rh/HT was demon-
strated by a one-pot synthesis of 3,3-diarylnitrile from
Ebitani, K.; Kaneda, K. Tetrahedron Lett. 2002, 43, 6229;
Oxidation of alcohols: (c) Kaneda, K.; Yamashita, T.;
Matsushita, T.; Ebitani, K. J. Org. Chem. 1998, 63, 1750;
(d) Matsushita, T.; Ebitani, K.; Kaneda, K. Chem.
Commun. 1999, 265; (e) Ebitani, K.; Motokura, K.;
Mizugaki, T.; Kaneda, K. Angew. Chem., Int. Ed. 2005,
2
, benzaldehyde, and ethyl cyanoacetate. After the com-
pletion of the aldol reaction of ethyl cyanoacetate with
benzaldehyde catalyzed by surface base sites on the
HT, further reaction with 2 in the same reactor afforded
4
4, 3423; One-pot synthesis: (f) Motokura, K.; Nishimura,
2
-cyano-3,3-diphenyl propionate, an important precur-
1
9
D.; Mori, K.; Mizugaki, T.; Ebitani, K.; Kaneda, K.
J. Am. Chem. Soc. 2004, 126, 5662; (g) Motokura, K.;
Mizugaki, T.; Ebitani, K.; Kaneda, K. Tetrahedron Lett.
sor of (2R)-3,3-diphenyl-2-methylalanine, in 74% over-
all yield (Scheme 3).
2
0
2
004, 46, 6029; (h) Motokura, K.; Fujita, N.; Mori, K.;
Mizugaki, T.; Ebitani, K.; Kaneda, K. Tetrahedron Lett.
005, 46, 5507; (i) Motokura, K.; Fujita, N.; Mori, K.;
In conclusion, we have demonstrated that the Rh/HT
acts as an efficient catalyst for the 1,4-addition reaction
of organoboron reagents to various a,b-unsaturated car-
bonyl compounds in the presence of 1,5-cod. The advan-
tages of this reaction system include (i) high catalytic
activity and selectivity, (ii) applicability toward diverse
sets of substrates, (iii) simple work-up and catalyst reus-
ability, and (iv) the possibility of one-pot synthesis. This
Rh/HT catalyst could act as a pivotal tool in the devel-
opment of economically and environmentally friendly
carbon–carbon bond forming reactions.
2
Mizugaki, T.; Ebitani, K.; Kaneda, K. J. Am. Chem. Soc.
2005, 127, 9674.
6. Sakai, M.; Hayashi, H.; Miyaura, N. Organometallics
1997, 16, 4229.
7
. Asymmetric 1,4-addition to enones: (a) Takaya, Y.;
Ogasawara, M.; Hayashi, T.; Sakai, M.; Miyaura, N.
J. Am. Chem. Soc. 1998, 120, 5579; (b) Hayashi, T.;
Takahashi, M.; Takaya, Y.; Ogasawara, M. J. Am. Chem.
Soc. 2002, 124, 5052; (c) Hayashi, T.; Ueyama, K.;
Tokunaga, N.; Yoshida, K. J. Am. Chem. Soc. 2003,
1
25, 11508; (d) Defieber, C.; Paquin, J.-F.; Serna, S.;
Carreira, E. M. Org. Lett. 2004, 6, 3873; (e) Otomaru, Y.;
Okamoto, K.; Shintani, R.; Hayashi, T. J. Org. Chem.
Acknowledgements
2
005, 70, 2503.
8
9
. 1,2-Addition to aldehydes: (a) Sakai, M.; Ueda, M.;
Miyaura, N. Angew. Chem., Int. Ed. 1998, 37, 3279; (b)
Ueda, M.; Miyaura, N. J. Org. Chem. 2000, 65, 4450; (c)
Fr u¨ stner, A.; Krause, H. Adv. Synth. Catal. 2001, 343,
This investigation was supported by Grant-in-Aid
for Scientific Research from Ministry of Education,
Culture, Sports, Science, and Technology of Japan
(
16206078). We thank Dr. Tomoya Uruga and Dr. Ha-
jime Tanida at JASRI Spring-8 for XAFS measurement
2005B0493) and the center of excellence (21COE; pro-
3
43.
. Friedel–Crafts acylation with organoboron reagents:
Frost, C. G.; Wadsworth, K. J. Chem. Commun. 2001,
2316.
(
gram ‘Creation of Integrated Ecochemistry’, Osaka
University). We are also grateful to the Department of
Materials Engineering Science, Graduate School of
Engineering Science, Osaka University, for scientific
support with the gas-hydrate analyzing system (GHAS).
K.M. thanks the JSPS Research Fellowship for Young
Scientists.
10. Phosphinated polystyrene-bound Rh catalyst for 1,4-
addition was reported; see: Otomaru, Y.; Senda, T.;
Hayashi, T. Org. Lett. 2004, 6, 3357.
1
1
1
3 2
1. HT [Mg0.827Al0.173(OH)1.930(CO )0.090(Cl)0.063Æ0.62H O]
was obtained from Tomita Pharmaceutical Co., Ltd.
2. For recent examples of 1,4-addition reactions using Rh-
diene complex catalysts; see Refs. 7c–e.
3. Karageorge, G. N.; Bertenshaw, S.; Iben, L.; Xu, C.;
Sarbin, N.; Gentile, A.; Dubowchik, G. M. Bioorg. Med.
Chem. Lett. 2004, 14, 5881.
References and notes
1
4. For the large-scale reaction, 1 (12 mmol), 2 (12 mmol),
Rh/HT (0.030 g, Rh: 0.006 mmol), 1,5-cod (0.006 mmol),
and 1,4–dioxane (20 mL) were used. The reaction mixture
was vigorously stirred at 100 ꢁC under Ar for 12 h. After
the reaction, the catalyst was removed by filtration, and
the filtrate was evaporated. The crude product was
purified by silicagel column chromatography (n-hexane/
ethyl acetate, 9:1), thus affording 3 as a colorless oil (81%
isolated yield).
1
. Balogh, M.; Laszlo, P. Organic Chemistry Using Clays;
Springer-Verlag: New York, 1993; Clark, J. H. Catalysis
of Organic Reactions by Supported Inorganic Reagents;
VHC: New York, 1994; Augustine, R. L. Heterogeneous
Catalysis for the Synthetic Chemist; Dekker: New York,
1996.
2
3
. For review of HT catalysts, see: Sels, B. F.; De Vos, D. E.;
Jacobs, P. A. Catal. Rev. 2001, 43, 443.
. Recent examples of HT-supported transition metal cata-
lysts: (a) Sels, B.; De Vos, D.; Buntinx, M.; Pierard, F.;
Kirsch-De Mesmaeker, A.; Jacobs, P. Nature 1999, 400,
15. During the preparation of our manuscript, a high perfor-
mance homogeneous rhodium catalyst (TOF = 14,000) for
the 1,4-addition of arylboroxines to a,b-unsaturated
ketones was reported. See: Chen, F.-X.; Kina, A.; Haya-
shi, T. Org. Lett. 2006, 8, 341.
16. In each recycling experiment, 1,5-cod was added.
17. During adsorption of metal species onto the HT surface,
the strong surface basicity of the HT may induce forma-
tion of metal hydroxide species; see Refs. 5e,f.
855; (b) Kakiuchi, N.; Maeda, Y.; Nishimura, T.; Uemura,
S. J. Org. Chem. 2001, 66, 6620; (c) Choudary, B. M.;
Chowdari, N. S.; Karangula, J.; Kantam, M. L. J. Am.
Chem. Soc. 2002, 124, 5341.
. Base catalysis of HTs: (a) Kantam, M. L.; Choudary, B.
M.; Reddy, C. V.; Rao, K. K.; Figueras, F. Chem.
4

N. Fujita et al. / Tetrahedron Letters 47 (2006) 5083–5087
8. In FT of k -weighted Rh K-edge EXAFS of
5087
3
1
a
(2 mL) was vigorously stirred at 60 ꢁC under Ar
for 1 h. Then, 2 (1.5 mmol) was then added to the same
flask, and allowed to further react at 100 ꢁC under Ar
for 8 h. After the reaction, the catalyst was separated
by filtration. The filtrate was evaporated and the crude
product was purified by column chromatography
using silica (n-hexane/ethyl acetate, 9:1) to afford a pure
ethyl 2-cyano-3,3-diphenylpropionate (74% isolated
yield).
recovered Rh/HT after the reaction without 1,5-cod,
peaks due to Rh–Rh bonds appeared at around
˚
2
.4 A, which suggested the formation of Rh clusters.
1
2
9. Cativiela, C.; Diaz-de-Vlllegas, M. D.; Galevez, J. A.
Tetrahedron 1994, 50, 9837.
0. In a three-component reaction, a mixture of benzaldehyde
(
1 mmol), ethyl cyanoacetate (1 mmol), Rh/HT (0.060 g,
Rh: 0.012 mmol), 1,5-cod (0.012 mmol), and 1,4-dioxane