Selective hydroformylation of internal acetylenes by PdCl2(PCy3)2: Remarkable synergistic effect of cobalt [4]

Full text of DOI:10.1021/ja9703887

6448
J. Am. Chem. Soc. 1997, 119, 6448-6449
Selective Hydroformylation of Internal Acetylenes
cyclohexyl) catalyzes the selective hydroformylation of internal
acetylenes to give the corresponding R,â-unsaturated aldehydes
and (ii) the use of the PdCl2(PCy3)2-Co2(CO)8 bimetallic
catalyst system significantly improves the catalytic activity
without lowering the selectivity.
by PdCl
2
(PCy
3
)
2
: Remarkable Synergistic Effect of
1
Cobalt
Youichi Ishii, Kenya Miyashita, Kenji Kamita, and
Masanobu Hidai*
Preliminary examination of the hydroformylation of 4-octyne
(
1a, R ) C3H7) with the catalyst systems composed of PdCl2-
Department of Chemistry and Biotechnology
Graduate School of Engineering
The UniVersity of Tokyo
(PPh3)2 and/or metal carbonyls resulted in low selectivity (up
to 49% yield) of the unsaturated aldehyde 2a. In contrast, the
PdCl (PCy ) catalyst exhibited very high selectivity and
2
3 2
Hongo, Bunkyo-ku, Tokyo 113, Japan
moderate activity in the presence of NEt . The yield of 2a
3
reached 83% after 6 h (eq 1), and the formation of the saturated
ReceiVed February 5, 1997
We have long been interested in development of homoge-
neous heterobimetallic catalyst systems composed of two
different metal complexes which might be used for unique
organic synthesis. During our continuing study toward this
direction, we have developed several mixed-metal catalyst
systems for various types of carbonylation reactions including
2
3
the homologation of methanol, hydroformylation of olefins,
4
formylation of iodoarenes, and silylative carbonylation reactions
of iodoarenes. Such mixed-metal complex systems have now
1
aldehyde 3a and the simple hydrogenation product 4a was
almost negligible. Although the reaction proceeds at a relatively
high temperature (150 °C), this finding is of special interest,
because palladium complexes have received little attention as
catalysts for hydroformylation of olefins. Furthermore, the
combined use of PdCl2(PCy3)2 and Co2(CO)8 remarkably
improved the catalytic activity with little change of the
selectivity. Thus, by use of the Pd-Co bimetallic catalyst (Pd/
Co atomic ratio 1/1), the reaction was complete within 1 h, and
2a was obtained in 95% yield (Table 1). The stereochemistry
of the aldehyde was 95% E, which is compatible with the
common hydrometalation-carbonylation mechanism. Since
both Co2(CO)8 alone and Co2(CO)8-PCy3 are of low catalytic
activity and selectivity, it is obvious that palladium and cobalt
metals participate cooperatively in the selective production of
the unsaturated aldehyde. Table 1 also shows the effects of
other metal carbonyls as the second component of the catalyst.
Among them, Co2(CO)8 accelerated the reaction most ef-
fectively, but Fe3(CO)12 and W(CO)6 also brought about
unexpected enhancement of the reaction rate without lowering
the selectivity. In contrast, Rh4(CO)12 gave rise to formation
of a considerable amount of 3a, and other transition metal
carbonyls such as Cr(CO)6, Mo(CO)6, Mn2(CO)10, Re2(CO)10,
and Ru3(CO)12 exhibited no or small effects on the yields and
selectivities of the products.
become recognized as a promising tool in organic synthesis.
Actually, rates and/or selectivities of some synthetic reactions
have been significantly enhanced by effective cooperation of
two or more metal centers.5
The hydroformylation of olefins is one of the most important
industrial processes catalyzed by transition metal complexes,
6
and has therefore been extensively studied. On the other hand,
the hydroformylation of acetylenes to the R,â-unsaturated
aldehydes has met with little success.7 Most catalysts so far
reported have suffered from low selectivity and/or low yield of
the unsaturated aldehydes, primarily because the formation of
the corresponding saturated aldehydes and noncarbonylated
olefins can hardly be suppressed. However, Buchwald and co-
workers have reported very recently an effective catalyst
composed of Rh(CO)2(acac) (acac ) pentane-2,4-dionate) and
a special bisphosphite ligand.8 As an extension of our study
on hydroformylation of olefins catalyzed by Co-Ru mixed
3
systems, we have now surveyed various combinations of
transition metal complexes to achieve the hydroformylation of
acetylenes. Here we report that (i) PdCl2(PCy3)2 (Cy )
(
1) Homogeneous Multimetallic Catalysts. 12. Part 11: Misumi, Y.; Ishii,
Y.; Hidai, M. Organometallics 1995, 14, 1770.
2) Hidai, M.; Orisaku, M.; Ue, M.; Koyasu, Y.; Kodama, T.; Uchida,
Y. Organometallics 1983, 2, 292.
(
(3) (a) Hidai, M.; Fukuoka, A.; Koyasu, Y.; Uchida, Y. J. Chem. Soc.,
Changing the phosphine ligand of the palladium complex was
also found to dramatically influence the catalytic activity and
the product distribution. The use of bulky trialkylphosphines
such as PCy3 and P(i-Pr)3 was found to be essential to achieve
satisfactory activity, the former exhibiting the higher selectivity.
Catalysts with arylphosphines including PMe2Ph, PMePh2, and
bisphosphines of the type Ph2P(CH2)nPPh2 (n ) 1-4) were
much inferior in both activity and selectivity (13-62% yield
of 2a under the reaction conditions shown in Table 1). P(OPh)3
was totally ineffective as the ligand for the present Pd-Co
catalyst system. This makes a sharp contrast to the rhodium-
based catalyst reported by Buchwald, in which a bisphosphite
Chem. Commun. 1984 516. (b) Hidai, M.; Fukuoka, A.; Koyasu, Y.; Uchida,
Y. J. Mol. Catal. 1986, 35, 29. (c) Hidai, M.; Matsuzaka, H. Polyhedron
1
988, 7, 2369. (d) Ishii, Y.; Sato, M.; Matsuzaka, H.; Hidai, M. J. Mol.
Catal. 1989, 54, L13.
(
4) Misumi, Y.; Ishii, Y.; Hidai, M. J. Mol. Catal. 1993, 78, 1.
(
5) (a) Braunstein, P.; Rose, J. In Stereochemistry of Organometallic and
Inorganic Compounds; Bernal, I., Ed.; Elsevier: Amsterdam, 1989; Vol.
3
Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W.,
Eds.; Pergamon: Oxford, U.K., 1982; Vol. 6, pp 763-877. For other
pertinent examples, see: (c) Sawamura, M.; Sudoh, M.; Ito, Y. J. Am. Chem.
Soc. 1996, 118, 3309. (d) Wang, D.; Alper, H. J. Am. Chem. Soc. 1992,
, pp 3-138. (b) Roberts, D. A.; Geoffroy, G. L. In ComprehensiVe
1
14, 7018. (e) Brunet, J.-J.; de Montauzon, D.; Taillefer, M. Organometallics
1
991, 10, 341. Heterometallic clusters also serve as potential heterobimetallic
catalyst precursors. For such examples, see: (f) Wakabayashi, T.; Ishii,
Y.; Ishikawa, K.; Hidai, M. Angew. Chem., Int. Ed. Engl. 1996, 35, 2123.
ligand was adopted.
8
(g) Murata, T.; Mizobe, Y.; Gao, H.; Ishii, Y.; Wakabayashi, T.; Nakano,
The PdCl2(PCy3)2 and PdCl2(PCy3)2-Co2(CO)8 catalyst
systems were applicable to the hydroformylation of various
internal acetylenes. The results are summarized in Table 2. It
should be pointed out that the Pd-Co bimetallic catalyst is of
high efficiency and selectivity for the hydroformylation of
aliphatic acetylenes, but the reaction of diphenylacetylene (1e)
was accompanied by significant formation of stilbene (4e). The
hydrogenation product 4e seems to be caused mainly by cobalt
species, and this drawback could be avoided simply by
F.; Tanase, T.; Yano, S.; Hidai, M.; Echizen, I.; Nanikawa, H.; Motomura,
S. J. Am. Chem. Soc. 1994, 116, 3389. (h) Adams, R. D.; Barnard, T. S.;
Li, Z.; Wu, W.; Yamamoto, J. H. J. Am. Chem. Soc. 1994, 116, 9103.
(
6) Parshall, G. W.; Ittel, S. D. In Homogeneous Catalysis, 2nd ed.;
Wiley-Interscience: New York, 1992; pp 106-111.
7) (a) Doyama, K.; Joh, T.; Shiohara, T.; Takahashi, S. Bull. Chem.
Soc. Jpn. 1988, 61, 4353. (b) Campi, E. M.; Jackson, W. R. Aust. J. Chem.
989, 42, 471. (c)Nombel, P.; Lugan, N.; Mulla, F.; Lavigne, G. Organo-
metallics 1994, 13, 4673.
8) Johnson, J. R.; Cuny, G. D.; Buchwald, S. L. Angew. Chem., Int.
Ed. Engl. 1995, 34, 1760.
(
1
(
S0002-7863(97)00388-0 CCC: $14.00 © 1997 American Chemical Society

Communications to the Editor
J. Am. Chem. Soc., Vol. 119, No. 27, 1997 6449
Table 1. Hydroformylation of 4-Octyne Catalyzed by
PdCl (PCy ) and/or Metal Carbonyls
2 3 2
2c was obtained in 92% yield and cyclooctene was recovered
quantitatively. The chemoselectivity observed with these
catalysts leads to the selective hydroformylation of enynes.
When the hydroformylation of (Z)-1,4-diphenyl-1-buten-3-yne
was performed with the PdCl2(PCy3)2 catalyst (155 °C, 6 h),
a
GLC yield/%
catalyst
conv/%
2a
3a
4a
PdCl
PdCl
2
(PCy
(PCy
3
)
)
2
20
84
12
25
89
100
92
76
16
83
0
21
50
95
85
68
46
<1
<1
<1
2
24
2
0
<1
1
2
15
3
tr
tr
(2E,4Z)-2,5-diphenyl-2,4-pentadienal was obtained as the ex-
b
2
3
2
clusive carbonylation product (ca. 80% conversion, 39% isolated
yield).
Co
2
Co
2
Co
2
(CO)
(CO)
(CO)
8
8
8
c
-PCy
-PCy
3
3
b,c
The origin of the synergistic effect observed for the Pd-Co
system is of special interest. On the basis of fact that the product
selectivity of the bimetallic catalyst was similar to that observed
with the monometallic PdCl2(PCy3)2 catalyst, we consider that
chemical transformation of acetylenes mainly proceeds on a
palladium metal center and a cobalt species plays an important
role in accelerating at least a part of the palladium-catalyzed
cycle. We have previously observed that, in the reaction of
PdCl
PdCl
PdCl
PdCl
2
2
2
2
(PCy
(PCy
(PCy
(PCy
)
3 2
)
3 2
)
3 2
)
3 2
-Co
-W(CO)
-Fe (CO)12
-Rh (CO)12
2
(CO)
8
6
tr
tr
3
4
65
16
3
a
Reaction conditions: 4-octyne, 5 mmol; H
(PCy , 0.1 mmol; metal carbonyl, 0.1 mmol as metal atom;
benzene 5 mL; NEt
.2 mmol.
2
, 35 atm; CO, 35 atm;
, 3 mmol; 150 °C; 1 h. Reaction time, 6 h. c PCy
,
3
PdCl
2
3 2
)
b
3
0
-
PdPh(PMe3)2(O3SCF3) with [Co(CO)4] anion, facile CO inser-
tion into the Pd-C bond occurs to give the dinuclear benzoyl
Table 2. Hydroformylation of Internal Acetylenes Catalyzed by
9
a
complex (PMe3)2(PhCO)PdCo(CO)4. More recently Fukuoka
PdCl
2
(PCy
3
)
2
or PdCl
2
(PCy
3
)
2 2 8
-Co (CO)
and Komiya reported that the CO insertion into the Pd-C bond
GLC yield/%
in (dppe)MePdCo(CO)4 (dppe ) Ph2PCH2CH2PPh2) is much
acetylene
a (R ) n-C
b (R ) C
cat.b
conv/%
2
3
4
10
faster than that in PdMeCl(dppe). These facts suggest that
c
c
c
c
the cobalt metal in the present hydroformylation promotes the
CO insertion into the Pd-C bond of a vinylpalladium inter-
mediate to form an acylpalladium species. On the other hand,
a preliminary kinetic study showed that both the PdCl2(PCy3)2
and PdCl2(PCy3)2-Co2(CO)8 catalysts exhibited some depen-
dency of the reaction rates on the H2 pressure. This indicates
a mechanism in which the rate-determining step is the hydro-
genolysis of an acylpalladium intermediate to produce the
aldehyde, and the cobalt catalyst has a function to accelerate
the hydrogenolysis of the acyl-Pd bond. Indeed, this type of
1
1
1
1
1
1
3
H
7
)
A
A
A
A
A
B
100
96
97
95
99
94
95 (81)
88 (47)
90 (70)
95 (89)
2
3
2
2
0
0
3
3
5
2
30
15
2
H
5
)
c (R ) n-C
4
H
9
)
11
d (R ) n-C
e (R ) Ph)
5
H
)
d
e
53
f
g
c
h
e
77 (70)
a
b
For reaction conditions, see Table 1. A: PdCl
2
(PCy ) -Co
3
2
2
(CO)
CH Ph
CH Ph
8
,
c
d
e
B: PdCl
2
(PCy
3
)
2
.
Isolated yield in parentheses. 90% E. PhCH
2
2
f
g
h
was formed in 16% yield. Reaction time, 5 h. 92% E. PhCH
2
2
was formed in 2% yield.
rate enhancement has been revealed to operate in carbonylation
using the monometallic PdCl2(PCy3)2 catalyst, which produced
R-phenylcinnamaldehyde (2e) in 77% GLC yield. A similar
reaction of 1-phenyl-1-propyne (PdCl2(PCy3)2 catalyst, 155 °C,
3,4,11
reactions with heterobimetallic catalyst systems
modinuclear complex catalyst.
or a ho-
12
Although we must await
further investigation to elucidate the cooperative effects of the
palladium and cobalt metal centers, it is noteworthy that the
combined use of Co2(CO)8 with PdCl2(PCy3)2 showed remark-
ably favorable effects on the hydroformylation of acetylenes.
Further study on the mechanism and application of the novel
catalyst systems is actively underway.
6
h) resulted in the formation of a 3/2 mixture of 2-methyl-3-
phenyl-2-propenal and 2-phenyl-2-butenal in 83% total GLC
yield (>96% E) along with a small amount (<10%) of
propenylbenzenes.
One interesting feature of the PdCl2(PCy3)2 and PdCl2-
PCy3)2-Co2(CO)8 catalysts is their chemoselectivity. Thus,
when a 1:1 mixture of styrene and 1a was allowed to undergo
(
JA9703887
hydroformylation in the presence of the PdCl2(PCy3)2 catalyst
(
9) Misumi, Y.; Ishii, Y.; Hidai, M. J. Chem. Soc., Dalton Trans. 1995,
489.
10) Fukuoka, A.; Fukugawa, S.; Hirano, M.; Komiya, S. Chem. Lett.
(150 °C, 6 h), 1a was cleanly transformed into the unsaturated
3
aldehyde 2a (80% conversion, 78% yield), while styrene was
recovered almost quantitatively. No more than trace amounts
of hydrogenation and hydroformylation products of styrene were
observed. Furthermore, when a mixture of cyclooctene and 1c
was hydroformylated with the Pd-Co catalyst (150 °C, 1 h),
(
1997, 377.
(
11) Koyasu, Y.; Fukuoka, A.; Uchida, Y.; Hidai, M. Chem. Lett. 1985,
1
083.
(
12) Broussard, M. E.; Juma, B.; Train, S. G.; Peng, W.-J.; Laneman, S.
A.; Stanley, G. G. Science 1993, 260, 1784.