Immobilized Co/Rh heterobimetallic nanoparticle-catalyzed Pauson-Khand-type reaction

Article abstract of DOI:10.1002/adsc.200404298

Co/Rh heterobimetallic nanoparticles were prepared from cobalt-rhodium carbonyl clusters [Co₂Rh₂(CO)₁₂ and Co ₃Rh(CO)₁₂] and immobilized on charcoal. HR-TEM revealed that the size of the heterobimetal

Full text of DOI:10.1002/adsc.200404298

FULL PAPERS
Immobilized Co/Rh Heterobimetallic Nanoparticle-Catalyzed
Pauson–Khand-Type Reaction
Kang Hyun Park, Young Keun Chung*
Department of Chemistry, College of Natural Sciences, Seoul National University, Seoul 151-747, Korea
Fax: (þ82)-2-889-0310, e-mail: ykchung@plaza.snu.ac.kr
Received: September 9, 2004; Accepted: February 28, 2005
Abstract: Co/Rh heterobimetallic nanoparticles were Co2Rh2 catalyst was used as a catalyst in the Pauson–
prepared from cobalt-rhodium carbonyl clusters Khand-type reaction in the presence of an aldehyde
[Co2Rh2(CO)12 and Co3Rh(CO)12] and immobilized instead of carbon monoxide, the catalytic system
on charcoal. HR-TEM revealed that the size of the was highly efficient. When the reaction was carried
heterobimetallic nanoparticles was ca. 2 nm and out in the presence of chiral diphosphines, ee values
ICP-AES analysis showed a 2:2 and a 3:1 cobalt-rho- up to 87% were observed. The catalytic system can
dium stoichiometry (Co2Rh2 and Co3Rh1) in the het- be reused at least five times in the presence of chiral
erobimetallic nanoparticles. The Co/Rh heterobime- diphosphines without loss of catalytic activity and
tallic nanoparticles immobilized on charcoal were enantioselectivity. The addition of Hg(0), a known
used as a catalyst in the Pauson–Khand-type reaction heterogeneous catalyst poison, completely inhibits
under 1 atm of CO. The catalytic reactivity was highly further catalysis. Thus, an environmentally friendly
dependent upon the ratio of Co:Rh with the highest and sustainable process was developed.
reactivity being observed when the ratio was 2:2
(Co2Rh2). The Co2Rh2 immobilized catalyst is quite Keywords: aldehyde; asymmetric reaction; cobalt;
an effective catalyst for intra- and intermolecular heterogeneous catalyst; nanoparticles; Pauson–Khand
Pauson–Khand-type reactions. When the immobilized reaction; rhodium
Introduction
tallic complexes (Co/Mo and Co/W)[6] have been em-
ployed in the Pauson–Khand reaction. Recently, the
Metal nanoparticles are a subject of great interest in use of cobalt nanoparticles as catalysts was also reported
chemistry and materials science because they display by us.[7]
unusual physical and chemical properties, which are dis-
Compared to dicobalt octacarbonyl, cobalt nanoparti-
tinct from those of both the bulk phase and isolated mol- cles were quite active. However, when cobalt nanoparti-
ecules.[1] Their unique features can be tailored by alter- cles were used as a catalyst, the relatively high pressure
ing their size, the organization of the nanoparticle crys- (5 atm) of carbon monoxide was still an obstacle for use
tal lattice, and the microenvironment surrounding them. in an ordinary organic laboratory. Therefore, it is still
For noble metal nanoparticles, catalytic applications are necessary to develop a heterogeneous catalytic system
considered, since a unique combination of reactivity, for use under milder reaction conditions.
stability, and selectivity is expected. During the past dec-
Recently, the use of heterobimetallic nanoparticles as
ade, transition metal nanoparticles have been revealed catalysts has attracted much attention because their cat-
as very efficient catalysts for various reactions, such as alytic performance is generally superior to that of a sin-
hydrogenation, oxidation, coupling reactions, and gle nanometal by itself.[8] Thus, we decided to create het-
some photocatalytic reactions.[2]
erobimetallic nanoparticles and to study their catalytic
Since the initial discovery of the Pauson–Khand reac- activity in the Pauson–Khand-type reaction. What kinds
tion,[3] it has been extensively developed by numerous of heterobimetallic nanoparticles were suitable as cata-
researchers. In particular, the development of a catalytic lysts? Studies on homogeneous rhodium catalysts might
and asymmetric version of the Pauson–Khand reaction provide clues to the development of a heterogeneous
makes it one of the most convergent and versatile meth- catalytic system: when rhodium complexes were used
ods for the construction of 5-membered rings.[4] In the as catalysts for the Pauson–Khand reaction, the pressure
beginning, dicobalt octacarbonyl had been used, but re- was usually ꢀ1 atm.[9] Thus, we decided to prepare Co/
cently several other transition metal complexes[5] in- Rh heterobimetallic nanoparticles, immobilize them on
cluding Ti, Ru, Rh, Ir, Ni, Mo, and W, and heterobime- charcoal, and study the use of these immobilized Co/Rh
854
ꢀ 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/adsc.200404298
Adv. Synth. Catal. 2005, 347, 854–866

Nanoparticle-Catalyzed Pauson? Khand-Type Reaction
FULL PAPERS
nanoparticles on charcoal as a catalyst in the Pauson– heterobimetallic carbonyl compound was fully decom-
Khand-type reaction under 1 atm of carbon monoxide. posed to heterobimetallic nanoparticles. The evolution
Very recently, we reported the use of Co/Rh heterobi- of the decomposition of the heterobimetallic carbonyl
metallic nanoparticles in the carbonylative silylcarbo- compound can be monitored by FT-IR spectroscopy fol-
cyclization of 1,6-enynes and Pauson–Khand-type reac- lowing the distinct CO vibration peak. After removal of
tions between alkynes and a,b-unsaturated alde- all the solvent, the black precipitates were re-suspended
hydes.[10]
Recent increasing environmental awareness has made Pauson–Khand-type reaction.
in THF. The THF suspension was used asa catalyst in the
the use of carbon monoxide undesirable and prompted
Generally, immobilization of catalysts on a solid sur-
the search for an alternative process in which it is not face makes the work-up strikingly simple. Thus, we im-
used or a substitute is employed for carbon monoxide.[11] mobilized the Co/Rh heterobimetallic nanoparticles
Recently, the use of decarbonylated CO from formates on charcoal. In order to immobilize Co/Rh nanoparti-
or aldehydes has been utilized in the Pauson–Khand re- cles on charcoal, the THF solution of Co/Rh nanoparti-
action.[12] Thus, we also studied the use of the immobi- cles was refluxed with flame-dried charcoal in THF for
lized Co/Rh nanoparticles as a catalyst in the Pauson– 12 h. After cooling and filtration of the solution under
Khand-type reaction in the presence of a substitute for a nitrogen atmosphere, the precipitate was washed suc-
carbon monoxide.
cessively with diethyl ether, dichloromethane, acetone,
Here we report in detail the synthesis and use of im- and methanol and dried under vacuum. The immobi-
mobilized Co/Rh heterobimetallic nanoparticles on lized black precipitate was used as a catalyst in the Pau-
charcoal as a catalyst in the Pauson–Khand-type reac- son–Khand-type reaction. According to ICP-AES data
tion under 1 atm of CO and the Pauson–Khand-type re- of the immobilized Co/Rh heterobimetallic nanoparti-
action in the presence of aldehydes instead of carbon cles, the ratios of Co:Rh were 1.09:1 and 2.93:1, respec-
monoxide. An asymmetric intramolecular Pauson– tively. Thus, the method used in this study always gave
Khand-type reaction in the presence of a chiral diphos- fixed stoichiometric Co/Rh bimetallic nanoparticles.
phine and aldehyde is also described. To the best of our HR-TEM photographs of the immobilized Co/Rh hetero-
knowledge, such a heterogeneous catalytic system has bimetallic nanoparticles and the corresponding particle
not been reported previously.
size distribution histogram are shown in Figures 1 and 2,
respectively. HR-TEM shows that the diameter of the
resulting well-dispersed, isolated, and anchored bimet-
allic nanoparticles is approximately 2 nm. Due to their
small size, we could not characterize them any further.
We also prepared nanoparticles of cobalt (Co4) and
rhodium (Rh4) from Co4(CO)12 and Rh4(CO)12, respec-
tively. They also have the same diameter (ca. 2 nm).
Thus, more than half of the atoms in the nanoparticles
are exposed to reactant species in the reaction.[14,18]
Results and Discussion
Synthesis and Characterization of Co/Rh
Heterobimetallic Nanoparticles and their
Immobilization
In order to create bimetallic nanoparticles with a fixed
stoichiometry, we employed the strategy of decomposi-
tion of bimetallic organometallic cluster compounds; it The Pauson–Khand-Type Reaction under 1 atm of CO
would appear that the use of molecular cluster com-
pounds as precursors is one of the most attractive meth- We first investigated the use of nanoparticles as catalysts
ods available.[13–15] Johnson et al.[13,16] generated bimet- in the intramolecular Pauson–Khand reaction of allyl
allic nanoparticles by decarbonylation of mixed-metal propargyl ether. The results are summarized in Table 1.
carbonyl precursors such as [Ru5PtC(CO)15]2ꢁ, [Ru10 Under 1 atm of CO, no reaction was observed with co-
Pt2C2(CO)28]2ꢁ
,
[Ru6C(CO)16SnCl3]ꢁ,
[Pd6Ru6 balt nanoparticles (Co4) on charcoal, and 23% of the re-
(CO)24]2ꢁ, and [Ru12C2Cu4Cl2(CO)32]2ꢁ. Shapley et al. action product was obtained with rhodium nanoparti-
reported[15] the preparation of two different composi- cles (Rh4) on charcoal. When Co3Rh was used, the ex-
tions ofPt-Ru nanoparticles supported on carbons by re- pected product was obtained in 65% yield. The best re-
duction of the neutral precursors PtRu5C(CO)16 and Pt2 sult (87%) was obtained when Co2Rh2 was used as a cat-
Ru4(CO)18 at elevated temperature in a hydrogen at- alyst. Interestingly, when a mixture of colloidal cobalt
mosphere.
and rhodium nanoparticles was used as a catalyst under
The clusters Co2Rh2(CO)12 and Co3Rh(CO)12 were the same reaction conditions, only 12% of the product
prepared as previously reported.[17] A solution contain- was obtained. Thus, it seemed that there arose some syn-
ing the heterobimetallic carbonyl compound was inject- ergistic effects between cobalt and rhodium nanoparti-
ed into a solution of o-dichlorobenzene, oleic acid, and cles in the Co2Rh2 and Co3Rh nanoparticles. However,
trioctylphosphine oxide at 1808C. Heating the resulting the exact nature of the synergistic effects cannot be ex-
solution at 1808C for 2 h afforded a black solution. The plained right now. Further study will provide clues to
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Figure 1. HR-TEM images of (left) Co2Rh2 (scale bar¼5 nm), (right) Co3Rh (scale bar¼5 nm).
as a catalyst (Table 2). For the intramolecular Pauson–
Khand reaction, all the substrates including heteroa-
tom-tethered enynes gave high yields (81–92%). The
catalytic system is also effective for the intermolecular
Pauson–Khand reaction although the yields (59–68%)
are not comparable to those of the intramolecular reac-
tion. It has been reported[19] that catalytic and substoi-
chiometric reactions based on cobalt carbonyls in the
presence of additives such as phosphane sulfide and cy-
clohexylamine have been developed under 1 atm of CO.
These processes are, at least, as effective as those report-
ed here, especially in terms of the intermolecular Pau-
son–Khand cyclization. Many useful rhodium catalysts
have been developed under similar mild conditions.
However, they are generally less effective for the inter-
molecular Pauson–Khand reaction[5d] and cannot be
reused. Therefore, the Rh/Co bimetallic nanoparticles
overcome the disadvantages of homogeneous rhodium
catalysts.
Figure 2. Particle size distribution of Co2Rh2 nanoparticles.
the nature of the synergistic effects. Therefore, the bi-
metallic nanoparticles were more reactive than the sin-
gle nanometal on its own. Using Co2Rh2 as a catalyst, The Pauson–Khand-Type Reaction in the Presence of
the optimized reaction conditions were established as Aldehydes
1 atm of CO, 1308C, THF, and 18 h.
When Co2Rh2 nanoparticles immobilized on charcoal We first screened organic substrates that could be easily
were used as a catalyst, the yield was 88%. Thus, immo- decarbonylated by transition metals. Aldehydes and for-
bilization of Co2Rh2 nanoparticles did not retard their mates are good candidates for our purpose because they
catalytic activity. To inspect the recyclability, the immo- have been studied with this end in mind for three deca-
bilized Co2Rh2 was separated and reused several times. des.[20] Using Co3Rh or Co2Rh2 nanoparticles as catalyst,
When the catalyst was recycled, the catalyst was filtered, we screened aldehydes and formates as a substitute for
dried under vacuum, and reused for the following cata- carbon monoxide in an intramolecular Pauson–
lytic reaction. The results shown in Table 1 confirm the Khand-type reaction (Table 3). As shown in Table 3, al-
catalyst maintained its high level of activity even after dehydes were quite effective in giving a carbonylative
being recycled five times.
cycloaddition product, but 2-pyridylmethyl formate
Next we investigated the versatility of intra- and inter- was ineffective. Especially, a,b-unsaturated aldehydes
molecular Pauson–Khand reactions under the opti- such as cinnamaldehyde, crotonaldehyde, and acrolein
mized reaction conditions using immobilized Co2Rh2 produced good results but aryl aldehydes such as benzal-
856
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Table 1. Pauson–Khand reaction with various catalysts under 1atm of CO.[a]
Entry
Catalyst
Yield [%][b]
1
2
3
4
5
6
7
8
9
10
Co2Rh2
Co3Rh
87
65
0
23
12
88
89
96
87
87
Cobalt nanoparticles on charcoal
Rhodium nanoparticles on charcoal
A mixture of cobalt nanoparticles and rhodium nanoparticles
Co2Rh2 on charcoal
recovered from #6
recovered from #7
recovered from #8
recovered from #9
[a]
Reaction conditions: THF, 1 atm CO, 1308C, 18 h, Co2Rh2 (Co¼8.93 mg, Rh¼15.6 mg), Co3Rh (Co¼15.5 mg, Rh¼
9.03 mg), Co4 (24.5 mg), Rh4 (24.5 mg).
Yields of isolated product.
[b]
dehyde and 1-naphthaldehyde gave poor results. When molecular Pauson–Khand reaction products. In homo-
cinnamaldehyde was used, polystyrenes obtained as geneous catalysis using rhodium catalysts, phosphine
by-products had to be separated by column chromatog- has to be added to enhance the catalytic reaction.[21]
raphy. However, in the case of crotonaldehyde or acro- However, no additives were added to enhance or pro-
lein, propene or ethylene were produced and, accord- mote the catalytic reaction. Moreover, multi-gram
ingly, the purification of the Pauson–Khand reaction quantities of cyclopentenones were obtained without
products was much more routine. As for crotonaldehyde any difficulties.
and acrolein, the use of crotonaldehyde gave a slightly
Next we investigated the use of immobilized Co2Rh2
higher yield than acrolein. Thus, crotonaldehyde was nanoparticles in the intermolecular Pauson–Khand-
our choice as the CO source. When Co3Rh was used in- type reaction (Table 4). Immobilized Co2Rh2 nanoparti-
stead of Co2Rh2, the expected product was obtained in cles are effective for the intermolecular Pauson–Khand-
80% yield. Moreover, the use of immobilized Co2Rh2 type reaction although the yields were not high, partly
nanoparticles as catalysts gave the product in 93% yield. due to the trimerization of alkynes. When phenylacety-
After much experimentation, optimized reaction lene was used as an alkyne substrate with norbornene,
conditions were established as follows: immobilized two reactions, the Pauson–Khand reaction and the tri-
Co2Rh2 (0.05 g), enyne (0.96 mmol), crotonaldehyde merization of phenylacetylene, competed with each oth-
(2.4 mmol), THF, 1308C, and 18 h.
er. Thus, the Pauson–Khand reaction product and trime-
The most important advantage of heterogeneous cat- rization product were obtained in 64% and 23% yields
alysis over its homogeneous counterpart is the possibil- (R¼Ph), respectively. When trimethylsilylacetylene
ity of recovering the catalytic system. Thus, the reusabil- was used (again with norbornene) no trimerization of
ity of the catalytic system was tested for the intramolec- the acetylene was observed. However, the conversion
ular Pauson–Khand-type reaction of cinnamic aldehyde was rather moderate (43%). Overall, our catalytic sys-
with phenylacetylene by checking any leaching of cobalt tem is effective for the intra- and moderately effective
and rhodium from the charcoal surface. Elemental anal- for the intermolecular Pauson–Khand-type reactions.
ysis (by ICP-AES) of the reaction mixture after comple-
tion of the reaction showed that less than 0.1 ppm of co-
balt and rhodium species were leached. The maximum Asymmetric Catalytic Pauson–Khand-Type Reaction
reusability of the catalytic system was not tested. How- in the Presence of an Aldehyde
ever, the catalytic activity of Co2Rh2 nanoparticles was
retained for at least five runs.
We next investigated an asymmetric and catalytic intra-
We next screened various enyne substrates for the in- molecular Pauson–Khand-type reaction. Much atten-
tramolecular Pauson–Khand reaction under the opti- tion has been paid to the preparation of transition metal
mized reaction conditions. As shown, the catalytic sys- nanoparticles and their use in catalysis.[1,2] However,
tem is quite effective for giving high yields of the intra- much less attention has been paid to the combination
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Kang Hyun Park, Young Keun Chung
Table 2. Immobilized Co2Rh2-catalyzed Pauson–Khand reaction of various substrates under 1 atm of CO.[a]
FULL PAPERS
Entry
Substrates
Products
Yield [%][b]
1
2
R¼Bu
R¼Ph
82
92
3
4
R¼Bu
R¼Ph
89
87
5
6
R¼Me
R¼Bu
81
91
7
8
9
10
R¼Bu
60
63
65
68
R¼Ph
R¼TMS
R¼Cyclohexene-1-yl
11
59
[a]
Reaction conditions: THF, 1 atm CO, 1308C, 18 h.
Yields of isolated product.
[b]
of optically active ligands with transition metal nanopar- room temperature and the reaction product was isolat-
ticles. Very recently, Fujihara and Tamura reported[22] ed. As shown in Table 5, the presence of chiral ligands
the synthesis of chiral bisphosphine BINAP-stabilized does not harm the yield of the reaction. Moreover,
gold and palladium nanoparticles and their use in a cat- even when the lower quantities of catalyst were used
alytic asymmetric hydrosilylation of styrene. Enantio- (0.05 g), the yields were quite high (75–94%) but the
meric excesses of up to 75% were obtained at room tem- ee values were highly dependent upon the chiral ligand
perature and these increased to 95% when the hydrosi- itself. It has been documented[23] that the use of (S)-(þ)-
lylation was carried out at 08C.
2,2’-bis(diphenylphosphino)-1,1’-binaphthyl [(S)-BI-
First of all, we screened various C2-symmetrical chiral NAP] as a ligand was the most effective in cobalt-cata-
diphosphine ligands (Table 5). Enyne (0.96 mmol), cro- lyzed reactions of 1,6-enynes. The use of (R)-(þ)-2,2’-
tonaldehyde (2.4 mmol), chiral phosphinine ligand bis(diphenylphosphino)-1,1’-binaphthyl [(R)-BINAP]
(0.11 mmol), Co2Rh2 on charcoal (0.05 g), and THF (entry 1) as a chiral ligand gave an ee value of 79%. In-
(5 mL) were reacted in a stainless-steel bomb. After troduction of a methyl group to the phenyl group of (R)-
heating at 1308C for 18 h, the bomb was cooled to BINAP
[(R)-(þ)-2,2’-bis(di-p-tolylphophino)-1,1’-
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Table 3. Immobilized Co/Rh-catalyzed intramolecular Pau-
son–Khand reaction using a substitute for carbon monox-
ide.[a]
binaphthyl¼(R)-Tol-BINAP] (entry 2) did not assist in
raising the ee value (73%). When (R)-DIOP was used,
the ee value dropped to 34% (entry 3). Strangely, in
the case of (2R,3R)-(ꢁ)-2,3-bis(diphenylphosphino)-bi-
cyclo[2.2.1]hept-5-ene [(R,R)-NORPHOS], a racemate
was obtained (entry 4). However, surprisingly, the use
of
(2S,4S)-(ꢁ)-2,4-bis(diphenylphosphino)pentane
[(S,S)-BDPP] gave a high ee value of 84% (entry 5).
Considering both the yield and ee values, (S,S)-BDPP
was the best choice for the asymmetric Pauson–
Khand-type reaction. Thus, using (S,S)-BDPP as a chiral
ligand, other enyne substrates were subjected to the
Pauson-Khand reaction conditions (entries 6–12). The
yields were high (75–94%) and the ee values were mod-
erate to high (51–87%). The best ee value was 87% (en-
try 11). Interestingly, the ee values obtained were com-
parable to those obtained in homogeneous catalysis us-
ing rhodium catalysts derived from [RhCl(CO)2]2/(S)-
BINAP and AgOTf.[21] Especially, the 84% ee value
for enyne (entry 5) was greater than that (74%) obtained
with the homogeneous rhodium catalysis. At present, a
detailed mechanism for the asymmetric induction of
our catalytic system in the presence of chiral diphos-
phines cannot be proposed. Further study, including the-
oretical calculations, will provide some clues for the ra-
tionalization of the asymmetric induction.
Entry Ligand
Time [h] Yield [%][b]
1
2
3
4
5
6
7
8
9
10
Acrolein
18
18
18
18
18
18
87
91
93[c]
93
43
35
–
Crotonaldehyde
Crotonaldehyde
Cinnamaldehyde
Benzaldehyde
1-Naphthaldehyde
2-Pyridylmethyl formate 18
Crotonaldehyde
Crotonaldehyde
Crotonaldehyde
12
6
18
85
81
80[d]
[a]
[b]
[c]
[d]
Reaction conditions: THF, 1308C, and Co2Rh2.
Yields of isolated products.
Co2Rh2 immobilized on charcoal.
Co3Rh was used.
[a]
Table 4. Pauson–Khand reactions catalyzed by immobilized Co2Rh2.
Entry
Substrate
R
Yield [%][b]
1
2
3
4
5
6
7
8
X¼(MeO2C)2C
X¼(MeO2C)2C
X¼O
R¼Bu
90
97
85
93
87
90
65
64
43
70
63
49
17
R¼Ph
R¼Bu
X¼O
R¼Ph
X¼N-SO2C6H4-CH3-p
X¼N-SO2C6H4-CH3-p
Norbornene
Norbornene
Norbornene
R¼Me
R¼Bu
R¼Bu
R¼Ph
9
R¼TMS
R¼Cyclohexen-1-yl
R¼Ph
10
11
12
13
Norbornene
2,5-Norbornadiene
Cyclopentene
Cyclohexene
R¼Ph
R¼Ph
[a]
Reaction conditions: immobilized Co2Rh2 (0.05 g), enyne (0.96 mmol) for entries 1–6 or cyclic alkene (0.96 mmol) and
terminal alkyne (1.15 mmol) for entries 7–11, crotonaldehyde (2.4 mmol), THF, 1308C, and 18 h.
Yields of isolated products.
[b]
Adv. Synth. Catal. 2005, 347, 854–866
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Kang Hyun Park, Young Keun Chung
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Table 5. Immobilized Co2Rh2-catalyzed asymmetric Pauson–Khand reaction.[a]
Entry
Catalyst
Substrate
X
Ligand
Yield [%][b]
ee [%]
R
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Co2Rh2 on charcoal
Co2Rh2 on charcoal
Co2Rh2 on charcoal
Co2Rh2 on charcoal
Co2Rh2 on charcoal
Co2Rh2 on charcoal
Co2Rh2 on charcoal
Co2Rh2 on charcoal
Co2Rh2 on charcoal
Co2Rh2 on charcoal
Co2Rh2 on charcoal
Co2Rh2 on charcoal
recovered from # 5
recovered from # 13
recovered from # 14
recovered from # 15
O
O
O
O
O
O
O
Ph
Ph
Ph
Ph
(R)-BINAP
(R)-Tol-BINAP
(R)-DIOP
93
91
90
83
91
75
85
94
92
89
93
94
90
89
93
90
79
73
34
–
(R,R)-NORPHOS
(S,S)-BDPP
(S,S)-BDPP
(S,S)-BDPP
(S,S)-BDPP
(S,S)-BDPP
(S,S)-BDPP
(S,S)-BDPP
(S,S)-BDPP
(S,S)-BDPP
(S,S)-BDPP
(S,S)-BDPP
(S,S)-BDPP
Ph
84
62
80
85
56
64
87
51
85
80
83
84
Bu
CH3
Ph
CH3
Ph
CH3
Ph
Ph
N-SO2C6H4-CH3-p
(MeO2C)2C
(MeO2C)2C
(EtO2C)2C
(EtO2C)2C
O
O
O
O
Ph
Ph
Ph
[a]
Reaction conditions: 1,6-enyne (0.96 mmol), crotonaldehyde (2.4 mmol), L* (0.11 mmol), immobilized catalyst (0.05 g, to-
tal weight of metals¼12.2 mg), THF, 18 h, 1308C.
[b]
Yields of isolated products.
The reusability of the catalytic system was tested for dition and simultaneous coordination of diphosphine li-
the asymmetric Pauson–Khand-type reaction (entries gands, all within the coordination sphere of the metal?
5 and 13–16). For the recyclization, the catalyst ob- In order to obtain some evidence for distinguishing be-
tained by filtration was reused and the insufficient chiral tween homogeneous versus heterogeneous catalysis,
diphosphine was supplemented by new chiral diphos- we carried out a mercury-poisoning experiment.
phine. As shown, the yields and ee values were retained
The ability of added Hg(0) to poison metal(0) hetero-
over at least five runs; the maximum reusability has not geneous catalysts[25] by amalgamating the metal catalyst
been tested. Elemental analysis (by ICP-AES) of the re- or adsorbing onto its surface is the single most widely
action mixture after completion of the three runs used test of homogeneous versus heterogeneous cataly-
showed that 3.9 ppm of cobalt and 0.3 ppm of rhodium sis.[26] The suppression of catalysis by Hg(0) is evidence
species were detected.
for a heterogeneous catalyst; if Hg(0) does not suppress
In many cases,[24] chiral diphosphine ligands were oxi- catalysis, the implication is that the catalysis is homoge-
dized to phosphine oxides during reaction or separation. neous. The Hg(0)-poisoning experiment is easy to per-
However, (S,S)-BDPP was recovered in 87% yield from form, but is not definitive by itself, and not universally
the reaction mixture after completion of the first run. applicable because Hg(0) reacts with some single-metal
Thus, the recovered (S,S)-BDPP can be used in further complexes.[25,26] Thus, this test inherently provides nega-
reactions.
tive evidence (no poisoning) in cases where the catalyst
is homogeneous.
With standard reaction conditions for the Pauson–
Khand-type reaction, an experiment with Co2Rh2 was
started as described above: [(3-allyloxy)prop-1-ynyl]-
Mercury-Poisoning Experiment
It seemed that the asymmetric Pauson–Khand-type re- benzene (0.96 mmol), crotonaldehyde (2.4 mmol), and
action catalyzed by transition metal nanoparticles is Co2Rh2 on charcoal (50 mg, 12 mg of Co2Rh2) in THF
rather unusual. Is this chemistry truly heterogeneous, (5 mL) were reacted in a stainless-steel bomb. After
i.e., catalyzed only by cobalt/rhodium nanoparticles at- about 5 h, the reaction was stopped, ~320 equivs.
tached to the charcoal support? If so, then in addition (0.175 g) of Hg(0) (vs. Co2Rh2) were added, and the re-
tosuch an association with charcoal, how can cobalt/rho- action was then restarted. We used a large excess of
dium nanoparticles accommodate both an oxidative ad- Hg(0) in a well-stirred solution to ensure intimate con-
860
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Nanoparticle-Catalyzed Pauson? Khand-Type Reaction
FULL PAPERS
tact of the Hg(0) bead with the entire reactor. The addi- Preparation of M4 Nanoparticles
tion of Hg(0) completely eliminated further catalysis
To a two-neck flask were added o-dichlorobenzene (24 mL),
oleic acid (0.2 mL), and trioctylphosphine oxide (0.4 g). While
the solution was heated at 1808C, a solution of metal carbonyl,
Co2Rh2(CO)12 (1.0 g), Co3Rh(CO)12 (1.08 g), Co4(CO)12
(1.19 g) or Rh4(CO)12 (0.89 g), in 6 mL of o-dichlorobenzene
was injected into the flask. The resulting solution was heated
at 1808C for 2 h. After the solution was cooled, the solution
was concentrated to a volume of ca. 10 mL by distillation. To
the concentrated solution was added THF (200 mL). The prog-
ress of the decomposition of organometallic clusters can be
monitored by checking the disappearance of one of the CO
stretching frequencies: for Co2Rh2(CO)12: 2074, 2064, 2059,
2058, 2030 cmꢁ1; for Co3Rh(CO)12: 2066, 2059, 2056, 2037,
2031 cmꢁ1; for Co4(CO)12: 2065, 2055 cmꢁ1; for Rh4(CO)12:
(i.e., for the next 15 h over which it was monitored).
The yield for 5 h was 31% and for an additional 15 h af-
ter the addition of mercury it was 32%. This result is con-
sistent with and strongly supportive of heterogeneous
metal(0) catalysis.[25,27] Since the activity was completely
poisoned, the heterogeneous metal(0) catalyst is the
only active species present. A similar experiment in
the presence of chiral diphosphine was also carried
out. [(3-Allyloxy)prop-1-ynyl]benzene (0.96 mmol),
crotonaldehyde (2.4 mmol), (S,S)-BDPP (0.11 mmol),
and Co2Rh2 on charcoal (50 mg, 12 mg of Co2Rh2) in
THF (5 mL) were put in a stainless-steel bomb. The
yield and ee values for 5 h were 31% and 82% ee, respec-
tively, and for an additional 15 h after the addition of
mercury they were 32% and 79% ee, respectively.
Thus, Hg(0) completely eliminated further catalysis.
2075, 2043 cmꢁ1
.
Immobilization of M4 Nanoparticles on Charcoal
To a two-neck flask were added o-dichlorobenzene (24 mL),
oleic acid (0.2 mL), and trioctylphosphine oxide (0.4 g). While
the solution was heated at 1808C, a solution of metal carbonyl,
Co2Rh2(CO)12 (1.0 g), Co3Rh(CO)12 (1.08 g), Co4(CO)12
(1.19 g), or Rh4(CO)12 (0.89 g), in 6 mL o-dichlorobenzene
was injected into the flask. The resulting solution was heated
to 1808C for 2 h and then concentrated to a volume of 5 mL.
The concentrated solution was cooled to room temperature.
To the cooled solutionwere added 25 mL of THF. After the sol-
ution was well stirred for 10 min, flame-dried charcoal (2.0 g)
was added to the solution. After the resulting solution had
been refluxed for 12 h, the precipitates were filtered and wash-
ed with diethyl ether (20 mL), dichloromethane (20 mL), ace-
tone (20 mL), and methanol (20 mL). Vacuum drying gave a
black solid.
Conclusion
We have demonstrated the usefulness of the combina-
tion of cobalt and rhodium nanoparticles in the intra-
and intermolecular Pauson–Khand reactions under
mild conditions. We have also achieved the develop-
ment of environmentally safe, clean, and sustainable
chemical processes for the asymmetric catalytic Pau-
son–Khand reaction. Multi-grams of cyclopentenones
are obtained without any difficulties and the reuse of
the catalyst has become a reality. Efforts to further de-
lineate the asymmetric induction in asymmetric Pau-
son–Khand-type reactions and to validate its usefulness
in natural product synthesis are underway in our labora-
tories. We expect that our methodology can be extended
to other catalytic systems in the near future.
High Resolution Transmission Electron Microscopy
(HR-TEM)
Co/Rh heterobimetallic nanoparticles immobilized on char-
coal were investigated by transmission electron microscopy
(TEM) on a JEM 100C transmission microscope. The samples
were prepared by placing a drop of the solution on carbon-
coated Cu grids and allowing this to dry in air. Counting 200
particles from enlarged TEM images monitored the particle
size and size distribution.
Experimental Section
General Remarks
All reactions were conducted under nitrogen using standard
Schlenk-type flasks. Work-up procedures were done in air.
All solvents were dried and distilled according to standard
methods before use. THF was freshly distilled from sodium
benzophenone ketyl prior to use. Reagents were purchased
from Aldrich Chemical Co. and Strem Chemical Co. and
were used as received. 1H NMR spectra were obtained with a
Bruker 300 MHz spectrometer. Elemental analyses were
done at the National Center for Inter-University Research Fa-
cilities, Seoul National University. High resolution mass spec-
tra were obtained at Korea Basic Science Institute (Daegu).
High-performance liquid chromatography (HPLC) was con-
ducted using a Hewlett-Packard 1100. Optical rotations were
measured on a Jasco DIP360 instrument. Flash chromatogra-
phy was performed using Merck Silica Gel 60 (230–400 mesh).
Synthesis of Enynes
2-Allyl-2-(hept-2-ynyl)malonic acid dimethyl ester (entry 1
in Table 2):[5a] To a solution of NaH (0.358 g, 60% dispersion
in mineral oil) in 10 mL of THF was added dropwise a solution
of dimethyl allylmalonate (1.0 mL, 6.22 mmol) in THF
(10 mL) at 08C over a period of 15 min, and then the mixture
was stirred at room temperature until the evolution of hydro-
gen gas subsided. The mixture was cooled to 08C, and a solu-
tion of 1-bromohept-2-yne (1.30 g, 7.42 mL) in THF (5 mL)
was added dropwise over a period of 15 min. Stirring of the
mixture at room temperature for 12 h afforded a brown solu-
tion with a white solid precipitate. Water (20 mL) was added,
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861

Kang Hyun Park, Young Keun Chung
FULL PAPERS
and the organic layer was separated. The aqueous layer was ex-
tracted with ether (15 mL), and the combined organic layers
were washed with water (20 mL) and brine (20 mL), dried
over MgSO4, and concentrated under vacuum. The residue
was purified by column chromatography on silica gel (ether/
hexane, 10/90) to give the respective enyne; yield: 1.6 g
17.0 Hz, 1H), 5.29 (dd, J¼16.9, 1.3 Hz, 1H), 5.28 (dd, J¼9.8,
1.1 Hz, 1H), 4.29 (s, 2H), 3.77 (d, J¼6.5 Hz, 2H), 2.29 (s, 3H),
1.66 (s, 3H).
N-Allyl-N-(hept-2-ynyl)-4-methyl-benzenesulfonamide
(entry 6 in Table 2):[5a] The same procedure as the synthesis of
the enyne (entry 5 in Table 2) was applied except for using N-
hept-2-yn-1-yl-4-methyl-benzenesulfonamide instead of N-
1
(97%). H NMR (CDCl3): d¼5.69 (ddt, J¼16.8, 9.7, 6.8 Hz,
but-2-yn-1-yl-4-methylbenzenesulfonamide.
1H
NMR
1H), 5.18 (dm, J¼16.3 Hz, 1H), 5.09 (dm, J¼9.7 Hz, 1H),
3.73 (s, 6H), 2.80–2.73 (m, 4H), 2.16–2.10 (m, 2H), 1.42–
1.38 (m, 4H), 0.89 (t, J¼7.1 Hz, 3H).
(CDCl3): d¼7.59 (d, J¼8.5 Hz, 2H), 7.19 (d, J¼8.5 Hz, 2H),
5.58 (dm, J¼12.0 Hz, 1H), 5.19 (dd, J¼16.8, 1.2 Hz, 1H),
5.15 (dd, J¼9.7, 1.2 Hz, 1H), 4.01 (t, J¼2.3 Hz, 2H), 3.29 (d,
J¼6.7 Hz, 2H), 2.33 (s, 3H), 1.78 (tt, J¼6.7, 2.4 Hz, 2H),
1.2–1.19 (m, 4H), 0.80 (t, J¼7.1 Hz, 3H).
2-Allyl-2-(3-phenylprop-2-ynyl)malonic acid dimethyl
ester (entry 2 in Table 2):[5a] The same procedure as the syn-
thesis of the enyne (entry 1 in Table 2) was applied except using
(3-bromoprop-1-yn-1-yl)benzene instead of 1-bromohept-2-
yne. 1H NMR (CDCl3): d¼7.42–7.46 (m, 2H), 7.31–7.33 (m,
3H), 5.78 (m, 1H), 5.18 (dm, J¼16.4 Hz, 1H), 5.14 (dm, J¼
9.8 Hz, 1H), 3.74 (s, 6H), 2.69–2.63 (m, 4H).
Intra- and Intermolecular Pauson–Khand-Type
Reactions under 1 atm of CO Catalyzed by
Immobilized Co2Rh2 on Charcoal
1-Allyloxyhept-2-yne (entry 3 in Table 2):[5a] To a solution
of NaH (0.513 g, 60% dispersion in mineral) in THF (10 mL)
was added dropwise a solution of hept-2-yn-1-ol (1 g,
8.91 mmol) in THF (10 mL) at 08C over a period of 10 min,
and then the mixture was stirred at room temperature until
the evolution of hydrogen gas subsided. The mixture was
cooled to 08C, and a solution of allyl bromide (0.93 mL,
10.7 mmol) in THF (5 mL) was added dropwise over a period
of 10 min. The mixture was stirred at room temperature for
1 h. Water (20 mL) was added slowly at 08C, and the organic
layer was separated. The aqueous layer was extracted with
ether (15 mL), and the combined organic layers were washed
with water (20 mL) and brine (20 mL), dried over MgSO4,
and concentrated under vacuum,. The residue was purified
by column chromatography on silica gel (ether/hexane, 10/
General procedure for an intramolecular reaction (entries 1–
6 in Table 2): To a solution of an enyne (1.2 mmol) in 10 mL of
THF was added Co2Rh2 (0.05 g of the immobilized Co2Rh2).
The reactor was charged with 1 atm of CO and heated at
1308C for 18 h. After the reactor was cooled to room temper-
ature, the solution was filtered, concentrated, and the product
isolated and purified by chromatography on a silica gel column,
eluting with hexane and diethyl ether (v/v, 5:1).
General procedure for an intermolecular reaction (entries
7–11 in Table 2): The same procedure as the above reaction
was applied except using a cyclic alkene (0.96 mmol) and a ter-
minal alkyne (1.15 mmol) instead of enyne (1.2 mmol).
Recycling experiment: In order to recycle the catalyst, it was
filtered from the reaction mixture and dried in vacuum and
then reused for the further catalytic reaction.
1
90) to give the enyne; yield: 1.3 g (96%). H NMR (CDCl3):
d¼5.85 (ddt, J¼16.8, 10.2, 5.3 Hz, 1H), 5.18 (dm, J¼
16.8 Hz, 1H), 5.17 (dm, J¼9.9 Hz, 1H), 4.03 (t, J¼1.7 Hz,
2H), 3.98–4.03 (m, 2H), 2.15–2.13 (m, 2H), 1.39–1.45 (m,
4H), 0.89 (t, J¼7.1 Hz, 3H).
[(3-Allyloxy)prop-1-ynyl]benzene (entry 4 in Table 2):[28]
Thesame procedure as the synthesis of theenyne (entry 3 inTa-
ble 2) was applied except for using 3-phenylprop-2-yn-1-ol
benzene instead of hept-2-yn-1-ol. 1H NMR (CDCl3): d¼
7.44–7.48 (m, 2H), 7.29–7.34 (m, 3H), 5.95 (ddt, J¼17.3,
10.7, 5.4 Hz, 1H), 5.35 (dm, J¼18.1 Hz, 1H), 5.24 (dm, J¼
12.0 Hz, 1H), 4.39 (s, 2H), 4.14 (dm, J¼5.8 Hz, 2H).
Intramolecular Pauson–Khand-Type Reactions under
1 atm of CO Catalyzed by Transition Metal
Nanoparticles
The same procedure as the above reaction was applied except
using a solution of transition metal nanoparticles in THF in-
stead of immobilized Co2Rh2 on charcoal. When Co2Rh2,
Co3Rh, Co4, and Rh4 nanoparticles were used as a catalyst,
the catalyst solution was prepared by dispersing nanoparticles
[Co2Rh2 (Co¼8.9 mg, Rh¼15.6 mg), Co3Rh (Co¼15.5 mg,
Rh¼9.0 mg), Co4 (24.5 mg), and Rh4 (24.5 mg)] in 10 mL of
THF.
N-Allyl-N-(but-2-ynyl)-4-methylbenzenesulfonamide
(entry 5 in Table 2):[5a] To a solution of NaH (0.217 g, 60% dis-
persion in mineral oil) in 10 mL of THF was added dropwise a
solution of N-but-2-yn-1-yl-4-methylbenzenesulfonamide (1 g,
3.76 mmol) in DMF (10 mL) at 08C over a period of 10 min,
and then the mixture was stirred at room temperature until
the evolution of hydrogen gas subsided. The mixture was
cooled to 08C, and a solution of allyl bromide (0.39 mL,
4.5 mmol) in THF (5 mL) was added dropwise over a period
of 10 min. The mixture was stirred at room temperature for
1 h. Water (20 mL) was added slowly at 08C, and the organic
layer was separated. The aqueous layer was extracted with
ether (15 mL), and the combined organic layers were washed
with water (20 mL) and brine (20 mL), dried over MgSO4,
and concentrated under vacuum. The residue was purified by
column chromatography on silica gel (ether/hexane, 20/90) to
6-Butyl-5-oxo-3,3a,4,5-tetrahydro-1H-pentalene-2,2-di-
carboxylic acid dimethyl ester (entry 1 in Table 2):[29]1H NMR
(CDCl3): d¼3.78 (s, 3H), 3. 73 (s, 3H), 3.18 (s, 2H), 2.78–2.98
(m, 1H), 2.77 (dd, J¼11.9, 6.9 Hz, 1H), 2.59 (dd, J¼17.2,
6.0 Hz, 1H), 2.11–2.29 (m, 1H), 2.01–2.13 (m, 2H), 1.59 (dd,
J¼11.9, 12.0 Hz, 1H), 1.11–1.55 (m, 4H), 0.88 (t, J¼7.3 Hz,
3H); IR: nCO ¼1732 cmꢁ1
.
5-Oxo-6-phenyl-3,3a,4,5-tetrahydro-1H-pentalene-2,2-
dicarboxylic acid dimethyl ester (entry 2 in Table 2):[29] 1H
NMR (CDCl3): d¼7.22–7.54 (m, 5H), 3.79 (s, 3H), 3.69 (s,
3H), 3.60 (d, J¼18.7 Hz, 1H), 3.28 (d, J¼18.5 Hz, 1H), 3.00–
3.16 (m, 1H), 2.78–2.81 (m, 2H), 2.29 (dd, J¼18.0, 2.9 Hz,
1
give the enyne; yield: 1.05 g (91%). H NMR (CDCl3): d¼
7.71 (d, J¼8.1 Hz, 2H), 7.33 (d, J¼8.1 Hz, 2H), 5.79 (dm, J¼
1H), 1.67 (dd, J¼11.9, 11.8 Hz, 1H); IR: nCO ¼1735 cmꢁ1
.
862
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Nanoparticle-Catalyzed Pauson? Khand-Type Reaction
FULL PAPERS
6-Butyl-3a,4-dihydro-1H,3H-cyclopenta[c]furan-5-one
(entry 3 in Table 2):[29] 1H NMR (CDCl3): d¼4.49 (q, J¼
13.8 Hz, 2H), 4.29 (s, 1H), 3.15 (d, J¼2.1 Hz, 2H), 2.66–2.58
(m, 1H), 2.22–2.29 (m, 1H), 2.10–2.15 (m, 2H), 1.21–1.25
and the filtrate was evaporated to dryness. Chromatography
on a silica gel column eluting with hexane and diethyl ether
(v/v, 5:1) gave the product.
For an intermolecular reaction, the same procedure as the
above reaction was applied except using a cyclic alkene
(0.96 mmol) and a terminal alkyne (1.15 mmol) instead of an
enyne (0.96 mmol).
2-Phenyl-4,5,6,6a–tetrahydro-3aH-pentalen-1-one (en-
try 12 in Table 4):[32] 1H NMR (CDCl3): d¼7.69–7.63 (m,
2H), 7.60–7.22 (m, 4H), 3.35–3.09 (m, 1H), 2.70–2.68 (m,
(m, 4H), 0.90 (t, J¼6.6 Hz, 3H); IR: nCO ¼1732 cmꢁ1
.
6-Phenyl-3a,4-dihydro-1H,3H-cyclopenta[c]furan-5-one
(entry 4 in Table 2):[29] 1H NMR (CDCl3): d¼7.13–7.31 (m,
5H), 4.56 (d, J¼15.8 Hz, 1H), 4.44 (d, J¼15.8 Hz, 1H), 4.27
(dd, J¼14.2 Hz, 1H), 3.07–3.14 (m, 2H), 2.58–2.69 (m, 2H);
IR: nCO ¼1734 cmꢁ1
.
6-Methyl-2-(4-toluenesulfonyl)-2,3,3a,4-tetrahydro-1H-
cyclopenta[c]pyrrol-5-one (entry 5 in Table 2):[30] 1H NMR
(CDCl3): d¼7.75 (d, J¼8.1 Hz, 2H), 7.36 (d, J¼8.1 Hz, 2H),
4.27 (d, J¼16.5 Hz, 1H), 4.02–3.95 (m, 2H), 3.01 (br s, 1H),
2.64–2.54 (m, 2H), 2.22 (s, 3H), 2.07 (dd, J¼3.3 Hz, 1H),
1H), 1.52–1.12 (m, 6H); IR: nCO ¼1697 cmꢁ1
.
2-Phenyl-3a,4,5,6,7,7a–hexahydroinden-1-one (entry 13
in Table 4):[34] 1H NMR (CDCl3): d¼7.71–7.66 (m, 2H), 7.61
(d, J¼2.5 Hz, 1H), 7.41–7.22 (m, 3H), 2.69–2.60 (m, 1H),
2.48 (d, J¼3.6 Hz, 1H), 2.33 (d, J¼5.1 Hz, 1H), 2.23 (d, J¼
3.8 Hz, 1H), 1.78–1.51 (m, 2H), 1.39–1.21 (m, 2H), 1.19–
1.68 (s, 3H); IR: nCO ¼1730 cmꢁ1
.
6-Butyl-2-(4-toluenesulfonyl)-2,3,3a,4-tetrahydro-1H-
cyclopenta[c]pyrrol-5-one (entry 6 in Table 2):[12c] 1H NMR
(CDCl3): d¼7.78 (d, J¼8.2 Hz, 2H), 7.30 (d, J¼8.2 Hz, 2H),
5.19 (q, J¼14.0 Hz, 2H), 4.00 (t, J¼2.4 Hz, 2H), 3.79 (d, J¼
5.9 Hz, 2H), 2.42 (s, 3H), 2.01–1.92 (m, 2H), 1.31–1.24 (m,
1.00 (m, 1H), 1.00–0.91 (m, 1H); IR: nCO ¼1704 cmꢁ1
.
Synthesis of Multi-Gram Amounts of 6-Phenyl-3a,4-
dihydro-1H,3H-cyclopenta[c]furan-5-one
4H), 0.85 (m, 3H); IR: nCO ¼1700 cmꢁ1
.
2-Butyl-3a,4,5,6,7,7a–hexahydro-4,7-methanoinden-1-
one (entry 7 in Table 2):[12e] 1H NMR (CDCl3): d¼7.09 (t, J¼
1.2 Hz, 1H), 2.56 (s, 1H), 2.37 (s, 1H), 2.12–2.16 (m, 4H),
1.66 (m, 2H), 1.46 (m, 2H), 1.28 (s, 6H), 0.52–0.97 (m, 3H);
[(3-Allyloxy-prop-1-ynyl]benzene (1.72 g, 0.01 mol), crotonal-
dehyde (0.24 mol), Co2Rh2 on charcoal (0.05 g), and THF
(5 mL) were put in a stainless-steel bomb. The bomb was heat-
ed at 1308C for 18 h. After the solution was cooled, the solution
was filtered and the filtrate was evaporated to dryness. Chro-
matography on a silica gel column eluting with hexane and di-
ethyl ether (v/v, 5:1) gave the product; yield: 1.46 g (73%).
IR: nCO ¼1702 cmꢁ1
.
2-Phenyl-3a,4,5,6,7,7a–hexahydro-4,7-methanoinden-1-
one (entry 8 in Table 2):[31] 1H NMR (CDCl3): d¼7.66–7.71
(m, 2H), 7.61 (d, J¼2.5 Hz, 1H), 7.22–7.41 (m, 3H), 2.60–
2.69 (m, 1H), 2.48 (d, J¼3.6 Hz, 1H), 2.33 (d, J¼5.1 Hz, 1H),
2.23 (d, J¼3.8 Hz, 1H), 1.51–1.78 (m, 2H), 1.21–1.39 (m,
2H), 1.00–1.19 (m, 1H), 0.91–1.00 (m, 1H); IR: nCO
¼
Competition Between a Trimerization and a Pauson–
Khand-Type Reaction
1699 cmꢁ1
.
2-Trimethylsilyl-3a,4,5,6,7,7a–hexahydro-4,7-metha-
noinden-1-one (entry 9 in Table 2):[32] 1H NMR (CDCl3): d¼
7.59 (d, J¼2.5 Hz, 1H), 6.27–6.31 (m, 2H), 2.77 (s, 1H),
2.69–2.71 (m, 3H), 2.50 (s, 1H), 1.89 (d, J¼6.3 Hz, 1H), 1.19
(d, J¼11.3 Hz, 1H), 0.98 (d, J¼11.3 Hz, 1H), ꢁ0.15 (s, 9H);
An alkyne (0.96 mmol), crotonaldehyde (2.4 mmol), Co2Rh2
on charcoal (0.05 g), and THF (5 mL) were put in a stainless-
steel bomb. The bomb was heated at 1308C for 18 h. After
this time, the solution was cooled and filtered, and the filtrate
was evaporated to dryness. Chromatography on a silica gel col-
umn eluting with hexane and diethyl ether (v/v, 10:1) gave the
Pauson–Khand product as major product and trimerization
product as minor product.
IR: nCO ¼1689 cmꢁ1
.
2-Cyclohex-1-en-1-yl-3a,4,5,6,7,7a–hexahydro-4,7-
methanoinden-1-one (entry 10 in Table 2):[12e] 1H NMR
(CDCl3): d¼7.22 (d, J¼4.8 Hz, 1H), 6.81 (d, J¼3.7 Hz, 1H),
2.88–2.92 (m, 1H), 2.51 (m, 1H), 2.21–2.22 (m, 4H), 1.57–
1.64 (m, 8H), 1.22–1.28 (m, 2H), 1.17 (m, 1H), 0.88 (m, 1H);
1,2,4-Tributylbenzene:[34,35] Yield: 21%; 1H NMR (CDCl3):
d¼6.89–7.10 (m, 3H), 2.10 (m, 6H), 1.38 (m, 12H), 0.86 (t,
J¼7.1 Hz, 9H).
IR: nCO ¼1708 cmꢁ1
.
1,2,4-Triphenylbenzene:[36] Yield: 23%; 1H NMR (CDCl3):
d¼7.14–7.20, (m, 9H), 7.31–7.65 (m, 5H), 7.61–7.68 (m, 4H).
2-Phenyl-3a,4,7,7a–tetrahydro-4,7-methanoinden-1-one
(entry 11 in Table 2):[33] 1H NMR (CDCl3): d¼7.71–7.65 (m,
3H), 7.36–7.31 (m, 3H), 6.29 (dd, J¼5.6, 3.2 Hz, 1H), 6.28
(dd, J¼5.6, 3.2 Hz, 1H), 3.02 (br s, 1H), 2.83 (m, 1H), 2.78
(br s, 1H), 2.46 (d, J¼5.4 Hz, 1H), 1.43 (d, J¼9.3 Hz, 1H),
1.33 (d, J¼9.3 Hz, 1H); IR: nCO ¼1699 cmꢁ1
.
Asymmetric Intramolecular Pauson–Khand-Type
Reaction Catalyzed by Immobilized Co2Rh2
An enyne (0.96 mmol), crotonaldehyde (2.4 mmol), chiral
phosphinine ligand (0.11 mmol), Co2Rh2 on charcoal (0.05 g),
and THF (5 mL) were put in a stainless-steel bomb. The
bomb was heated at 1308C for 18 h. After the reactor was
cooled to room temperature, the solution was filtered and
the filtrate was evaporated to dryness. Chromatography on a
silica gel column eluting with hexane and diethyl ether (v/v,
5:1) gave the product and intact chiral diphosphine. For the re-
cyclization, the catalyst obtained by filtration was reused and
Intra- and Intermolecular Pauson–Khand-Type
Reaction in the Presence of an Aldehyde Catalyzed by
Immobilized Co2Rh2 on Charcoal
For an intramolecular reaction, an enyne (0.96 mmol), croto-
naldehyde (2.4 mmol), Co2Rh2 on charcoal (0.05 g), and THF
(5 mL) were put in a stainless-steel bomb. The bomb was heat-
ed at 1308C for 18 h. After this time, the solution was cooled
Adv. Synth. Catal. 2005, 347, 854–866
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Kang Hyun Park, Young Keun Chung
FULL PAPERS
the insufficient chiral diphosphine was supplemented by new
chiral phosphine.
5-Oxo-6-phenyl-3,3a,4,5-tetrahydro-1H-pentalene-2,2-
dicarboxylic acid dimethyl ester (entry 10 in Table 5):[21]
Yield: 89%, [a]2D0: þ30.1 (c 1.3 in CH2Cl2), CHIRALPAC
AS: 64% ee, 2-propanol/hexane¼15/85, flow rate¼1 mL/
1
min, 1st product¼11.70 min, 2nd product¼14.53 min. The H
NMR spectrum matched the published spectrum.
Determination of Enantiomeric Purity
6-Methyl-5-oxo-3,3a,4,5-tetrahydro-1H-pentalene-2,2-
dicarboxylic acid diethyl ester (entry 11 in Table 5):[37] Yield:
93%, [a]2D0: þ85.6 (c 0.58 in CH2Cl2), CHIRALPAC OD-H:
87% ee, 2-propanol/hexane¼10/90, flow rate¼1 mL/min, 1st
product¼6.53 min, 2nd product¼7.43 min. The 1H NMR spec-
trum matched the published spectrum.
5-Oxo-6-phenyl-3,3a,4,5-tetrahydro-1H-pentalene-2,2-
dicarboxylic acid diethyl ester (entry 12 in Table 5):[36] Yield:
94%, [a]2D0: þ43.9 (c 0.58 in CH2Cl2), CHIRALPAC AS: 51%
ee, 2-propanol/hexane¼10/90, flow rate¼1 mL/min, 1st
peak¼8.88 min, 2nd peak¼12.37 min. The 1H NMR spectrum
matched the published spectrum.
The enantiomeric excesses (% ee) were determined by chiral
HPLC analysis. For entries 1, 2, 3, 4, 5, 6, 7, 9, 10, 12, 13, 14,
15 and 16 in Table 5, a CHIRALPAK AS 25 cmꢂ0.46 cm col-
umn (Daicel Chemical Ind., Ltd.) was used. For entry 8 in Ta-
ble 5, a CHIRALPAK AD 25 cmꢂ0.46 cm column (Daicel
Chemical Ind., Ltd.) was used. For entry 11 in Table 5, a CHIR-
ALPAK OD-H 25 cmꢂ0.46 cm column (Daicel Chemical
Ind., Ltd.) was employed.
6-Phenyl-3a,4-dihydro-1H,3H-cyclopenta[c]furan-5-one
(entry 1 in Table 5):[21] Yield: 93%, [a]2D0: ꢁ12.9 (c 1.80 in
CH2Cl2); CHIRALPAC AS: 79% ee, 2-propanol/hexane¼
10/90, flow rate¼1 mL/min, 1st product¼15.82 min, 2nd
product¼17.91 min. The 1H NMR spectrum matched the pub-
lished spectrum.
6-Phenyl-3a,4-dihydro-1H,3H-cyclopenta[c]furan-5-one
(entry 2 in Table 5):[21] Yield: 91%, [a]2D0: ꢁ9.1 (c 1.50 in
CH2Cl2); CHIRALPAC AS: 73% ee, I2-propanol/hexane¼
10/90, flow rate¼1 mL/min, 1st product¼15.53 min, 2nd ICP-AES Analysis
product¼17.44 min. The 1H NMR spectrum matched the pub-
Co and Rh contents were determined using inductive coupled
lished spectrum.
plasma atomic emission spectroscopy (ICP-AES) with the Shi-
madzu ICPS-1000 IV device. The analysis showed that the co-
balt-to-rhodium ratios were 1.09 for Co2Rh2 and 2.93 for
Co3Rh, respectively. When an ICP-AES analysis of the reac-
tion mixture after completion of the reaction of crotonalde-
hyde with phenylacetylene was carried out, the contents of co-
balt and rhodium were beyond the detection limit. For the test
of the reusability of the catalytic asymmetric system (entries 5
and 13–16 Table 5), an ICP-AES experiment (elemental anal-
ysis) on the reaction mixture after completion of the three runs
was carried out. The analysis showed that 3.9 ppm of cobalt and
0.3 ppm of rhodium species were present.
6-Phenyl-3a,4-dihydro-1H,3H-cyclopenta[c]furan-5-one
(entry 3 in Table 5):[21] Yield: 90%, [a]2D0: ꢁ2.8 (c 1.3 in
CH2Cl2), CHIRALPAC AS: 34% ee, 2-propanol/hexane¼
10/90, flow rate¼1 mL/min, 1st product¼15.80 min, 2nd
product¼17.68 min. The 1H NMR spectrum matched the pub-
lished spectrum.
6-Phenyl-3a,4-dihydro-1H,3H-cyclopenta[c]furan-5-one
(entry 5 in Table 5):[21] Yield: 91%, [a]2D0: ꢁ10.3 (c 1.50 in
CH2Cl2), CHIRALPAC AS: 84%ee, 2-propanol/hexane¼10/
90, flow rate¼1 mL/min, 1st product¼15.75 min, 2nd
product¼17.66 min. The 1H NMR spectrum matched the pub-
lished spectrum.
6-Butyl-3a,4-dihydro-1H,3H-cyclopententa[c]furan-5-
one (entry 6 in Table 5):[21] Yield: 75%, [a]2D0: ꢁ32.1 (c 1.11 in
CH2Cl2), CHIRALPAC AS: 62% ee, 2-propanol/hexane¼5/
95, flow rate¼0.9 mL/min, 1st product¼10.26 min, 2nd
product¼11.89 min. The 1H NMR spectrum matched the pub-
lished spectrum.
6-Methyl-3a,4-dihydro-1H,3H-cyclopenta[c]furan-5-one
(entry 7 in Table 5):[21] Yield: 85%, [a]2D0: ꢁ79.3 (c 0.90 in
CH2Cl2), CHIRALPAC AS: 80% ee, 2-propanol/hexane¼
10/95, flow rate¼1 mL/min, 1st product¼9.73 min, 2nd
product¼10.53 min. The 1H NMR spectrum matched the pub-
lished spectrum.
Mercury-Poisoning Experiment
Two batches were prepared for the experiment. The same
amounts of enyne, crotonaldehyde, and chiral diphosphine
were used for each experiment: [(3-allyloxy)prop-1-ynyl]ben-
zene (0.96 mmol), crotonaldehyde (2.4 mmol), (S,S)-BDPP
(0.11 mmol), and Co2Rh2 on charcoal (50 mg, 12 mg of
Co2Rh2) in THF (5 mL) were put in a stainless-steel bomb.
The bomb was heated at 1308C for 5 h. After the reactor had
cooled to room temperature, the solution was filtered and
the filtrate was evaporated to dryness. Chromatography on a
silica gel column eluting with hexane and diethyl ether (v/v,
5:1) gave the product in 31% yield with 82% ee.
6-Phenyl-2-(4-toluenesulfonyl)-2,3,3a,4-tetrahydro-1H-
cyclopenta[c]pyrrol-5-one (entry 8 in Table 5):[21] Yield: 94%,
[a]2D0: þ95.7 (c 0.57 in CH2Cl2), CHIRALPAC AD: 85% ee, 2-
propanol/hexane¼20/80,
flow
rate¼0.9 mL/min,
1st
product¼17.75 min, 2nd product 22.66 min. The 1H NMR
¼
spectrum matched the published spectrum.
For the mercury-poisoning experiment, the same procedure
as above was applied except that the addition of Hg (0.175 g,
320 equivs. to Co2Rh2 used) was made after heating the reactor
for 5 h. After the addition of Hg, the reactor was heated for
15 h. The usual purification procedure gave the product in
32% yield with 79% ee.
6-Methyl-5-oxo-3,3a,4,5-terahydro-1H-pentalene-2,2-di-
carboxylic acid dimethyl ester (entry 9 in Table 5):[23b] Yield:
92%, [a]2D0: þ57.5 (c 0.80 in CH2Cl2), CHIRALPAC AS:
56% ee, 2-propanol/hexane¼15/85, flow rate¼1 mL/min, 1st
product¼11.83 min, 2nd product¼14.12 min. The 1H NMR
spectrum matched the published spectrum.
864
ꢀ 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
Adv. Synth. Catal. 2005, 347, 854–866

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Acknowledgements
This work was supported by the Ministry of Science and Tech-
nology of Korea through the research Center for Nanocatalysis,
one of the National Science Programs for Key Nanotechnology.
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866
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Adv. Synth. Catal. 2005, 347, 854–866