Hexacarbonyldiplatinum(I) cation-catalyzed carbonylation of olefins in concentrated sulfuric acid

Full text of DOI:10.1021/jo000883c

J . Org. Chem. 2000, 65, 8105-8107
8105
Hexa ca r bon yld ip la tin u m (I)
Ca tion -Ca ta lyzed Ca r bon yla tion of Olefin s
in Con cen tr a ted Su lfu r ic Acid
Platinum catalysts have been used in many important
reactions, such as the hydroformylation and hydrosily-
lation of unsaturated compounds.2 In this paper, we
report the first example of the homoleptic, dinuclear,
cationic metal carbonyl catalyst, i.e., hexacarbonyldi-
,10
Qiang Xu,* Masahiro Fujiwara, Mutsuo Tanaka, and
Yoshie Souma
2
+
3 2 2 4
platinum(I), [{Pt(CO) } ] , in concd H SO , with which
olefins react with CO to produce tertiary carboxylic acids
in high yields at atmospheric pressure and room tem-
perature.
Osaka National Research Institute, AIST, MITI,
Midorigaoka, Ikeda, Osaka 563-8577, J apan
xu@onri.go.jp
Resu lts a n d Discu ssion
2
+
Received J une 9, 2000
F or m a tion of [{P t(CO) } ]
CO)
2
(1) a n d cis-P t-
(solv) (2) in Con cen tr a ted Su lfu r ic Acid . The
first homoleptic Pt(II) carbonyl complex, [Pt(CO) ][Pt-
SO F) ], was isolated by the reductive carbonylation of
Pt(SO
3
2
2
+
(
In tr od u ction
4
(
3
6
Since the discovery of the first metal carbonyls, Pt-
CO) Cl , Pt(CO)Cl , and Pt (CO) Cl , by Sch u¨ tzenberger
2 2 2 2 3 4
11d
3
4 3
F) in HSO F with CO at 25 °C. This reaction
represents the partial reduction of Pt(IV) by CO. Increas-
ing the reaction temperature from 25 °C to 80 °C results
in complete reduction to Pt(CO)
yellow intermediate, [Pt(CO) ][Pt(SO
reported that in SbF , the creamy white Pt(CO)
complex can be readily converted to the thermally stable,
(
1
in 1870, metal carbonyl complexes have played a very
important role in chemistry and the chemical industry.2
11a,b
2
(SO
3
F)
2
,
via the
For the typical metal carbonyls such as Ni(CO)
4
, Co
, the average vibrational frequen-
cies, ν(CO), are considerably lower than the value for free
2
-
4
3
F)
6
]. It has been
(SO F)
2
3
-
(
8 4
CO) , and Mn(CO)
5
2
3
-
1
CO, 2143 cm , mainly due to the strong metal-to-CO
π-back-bonding.3 Reactions catalyzed by such metal
carbonyls usually require high temperature and high
pressure.2
4 2 11 2
white salt, [Pt(CO) ][Sb F ] , in the presence of a CO
11c
atmosphere.
We have found that hexacarbonyldiplatinum(I), [{Pt-
2+
(
CO)
3
}
2
]
(1), the first homoleptic, dinuclear platinum-
Recently, there has been a rapid development in the
preparation and structural characterization of homoleptic
metal carbonyl cations and their cationic derivatives
ranging from groups 6 through 12,4,5 which, in contrast
to the typical metal carbonyl complexes, have a distin-
guishing characteristic in that the CO vibrational fre-
quencies are significantly increased; they have remark-
ably reduced π-back-bonding and reactive CO ligands.
Metal carbonyl cations have been employed as active
catalysts under very mild conditions. Cu(I), Ag(I), Au(I),
Pd(I), and Rh(I) carbonyls have been shown to be highly
(
I) carbonyl cation, is formed in concd H
2
SO
4
under a CO
12
atmosphere according to eq 1:
concd H SO
2
4
IV
+
I
2+
2
Pt O + 9CO + 2H
8 [{Pt (CO) } ]
+
2
3 2
rt, 1 atm
1
3CO + H O (1)
2
2
This involves a greater degree of reduction of Pt(IV)
than has been observed in superacids and must result
from the use of a less acidic medium. The reductive
active for the catalytic carbonylation of olefins in strong
carbonylation of PtO
2
by CO takes ca. 2 weeks in concd
acids at atmospheric pressure of CO.6 [Pt(CO
-8
)][Sb
F
]
2
H
SO at room temperature and atmospheric pressure
4
2
11
2
4
has recently been used for the stereospecific tetramer-
ization of 2-propynol and the polymerization of arylacety-
lenes.9
to go to completion and produce a colorless solution of 1.
Prolonged (ca. 1 day) evacuation of the solution of 1 in
concd H SO results in disproportionation and the ex-
2 4
*
To whom correspondence should be addressed. Phone: +81-727-
1-9652, Fax number: +81-727-51-9629.
1) (a) Sch u¨ tzenberger, P. C. R. Hebd. Seances Acad. Sci. 1870, 70,
(6) For a recent review, see: Xu, Q.; Souma, Y. Top. Catal. 1998, 6,
17.
(7) (a) Souma, Y.; Sano, H. Bull. Chem. Soc. J pn. 1976, 49, 3296.
(b) Souma, Y.; Sano, H. J . Org. Chem. 1973, 38, 3633. (c) Souma, Y.;
Sano, H.; Iyoda, J . J . Org. Chem. 1973, 38, 2016.
5
(
1
1
134. (b) Sch u¨ tzenberger, P. C. R. Hebd. Seances Acad. Sci. 1870, 70,
287. (c) Sch u¨ tzenberger, P. Bull. Chim. Fr. 1870, 14, 97.
(
2) For leading references, see: (a) Falbe, J ., Ed. New Syntheses with
(8) (a) Xu, Q.; Nakatani, H.; Souma, Y. J . Org. Chem. 2000, 65, 1540.
(b) Xu, Q.; Souma, Y.; Umezawa, J .; Tanaka, M.; Nakatani, H. J . Org.
Chem. 1999, 64, 6306. (c) Xu, Q.; Imamura, Y.; Fujiwara, M.; Souma,
Y. J . Org. Chem. 1997, 62, 1594.
Carbon Monoxide; Springer-Verlag: Berlin, 1980. (b) Colquhoun, H.
M.; Thompson, D. J .; Twigg, M. V. Carbonylation: Direct Synthesis of
Carbonyl Compounds; Plenum Press: New York, 1991.
(
3) (a) Barnes, L. A.; Rosi, M.; Bauschlicher, C. W., J r. J . Chem.
(9) Weber, L.; Barlmeyer, M.; Quasdorff, J .-M.; Sievers, H. L.;
Stammler, H.-G.; Neumann, B. Organometallics 1999, 18, 2497.
(10) (a) Bhaduri, S.; Mukesh, D. Homogeneous Catalysis: Mecha-
nisms and Industrial Applications; Wiley-Interscience: New York,
2000. (b) Cornils, B.; Herrmann, W. A., Eds. Applied Homogeneous
Catalysis with Organometallic Compunds; Wiley-VCH: Weinheim,
2000.
(11) (a) Ahsen, B. v.; Wartchow, R.; Willner, H.; J onas, V.; Aubke,
F. Inorg. Chem., submitted for publication. (b) Hwang, G.; Wang, C.;
Bodenbinder, M.; Willner, H.; Aubke, F. J . Fluorine Chem. 1994, 66,
159. (c) Hwang, G.; Wang, C.; Aubke, F.; Willner, H.; Bodenbinder,
M. Can. J . Chem. 1993, 71, 1532. (d) Hwang, G.; Bodenbinder, M.;
Willner, H.; Aubke, F. Inorg. Chem. 1993, 32, 4667.
Phys. 1991, 94, 2031. (b) Pierloot, K.; Verhulst, J .; Verbeke, P.;
Vanquickenborne, L. G. Inorg. Chem. 1989, 28, 3059. (c) Sherwood,
D. E., J r.; Hall, M. B. Inorg. Chem. 1980, 19, 1805. (d) Hall, M. B.;
Fenske, R. F. Inorg. Chem. 1972, 11, 1619.
(4) (a) Bernhardt, E.; Bley, B.; Wartchow, R.; Willner, H.; Bill, E.;
Kuhn, P.; Sham, I. H. T.; Bodenbinder, M.; Br o¨ chler, R.; Aubke, F. J .
Am. Chem. Soc. 1999, 121, 7188. (b) Br o¨ chler, R.; Freidank, D.;
Bodenbinder, M.; Sham, I. H. T.; Willner, H.; Rettig, S. J .; Trotter, J .;
Aubke, F. Inorg. Chem. 1999, 38, 3684. (c) Willner, H.; Aubke, F.
Angew. Chem., Int. Ed. Engl. 1997, 36, 2402.
(
5) (a) Polyakov, O. G.; Ivanova, S. M.; Gaudinski, C. M.; Miller, S.
M.; Anderson, O. P.; Strauss, S. H. Organometallics 1999, 18, 3769.
b) Luppinetti, A. J .; Strauss, S. H. Chemtracts-Inorg. Chem. 1998,
1, 565. (c) Hurlburt, P. K.; Rack, J . J .; Luck, J . S.; Dec, S. F.; Webb,
J . D.; Anderson, O. P.; Strauss, S. H. J . Am. Chem. Soc. 1994, 116,
0003.
(
1
(12) (a) Xu, Q.; Heaton, B. T.; J acob, C.; Mogi, K.; Ichihashi, Y.;
Souma, Y.; Kanamori, K.; Eguchi, T. J . Am. Chem. Soc. 2000, 122,
6862. (b) Xu, Q.; Souma, Y.; Heaton, B. T.; J acob, C.; Kanamori, K.
Angew. Chem., Int. Ed. 2000, 39, 208.
1
1
0.1021/jo000883c CCC: $19.00 © 2000 American Chemical Society
Published on Web 10/26/2000

8
106 J . Org. Chem., Vol. 65, No. 23, 2000
Notes
Ta ble 1. Hexa ca r bon yld ip la tin u m (I) Ca tion -ca ta lyzed
a
Ca r bon yla tion of Olefin s in Con cd H2SO4
substrate
tert-carboxylic acid
yield/%b
1
1
-pentene
-hexene
2,2-dimethylbutanoic
others
2,2-dimethylpentanoic
70
1
49
23
1
2
-methyl-2-ethylbutanoic
others
1
1
-octene
-decene
2,2-dimethylheptanoic
2-methyl-2-ethylhexanoic
43
20
11
2
39
20
11
3
F igu r e 1. Schematic structure of hexacarbonyldiplatinum(I)
2
+
cation, [{Pt(CO)
3
}
2
]
(1).
2
-methyl-2-propylpentanoic
others
clusive formation of the nearly colorless complex, cis-Pt-
2,2-dimethylnonanoic
2-methyl-2-ethyloctanoic
2
+
(
CO)
2
(solv) (2), according to eq 2:
2
2
-methyl-2-propylheptanoic
-methyl-2-butylhexanoic
-
4CO/concd H SO
2 4
2
+
(solv)
0
others
2
55
1
{+ 4CO/concd H2SO4} cis-Pt(CO)2
+ Pt
(2)
cyclohexene
1-methylcyclopentanecarboxylic
2
a
PtO2/substrate ) 2.0 mmol/5.0 mmol, 96% H2SO4 10 mL, CO
1
atm, rt. b Based on substrate.
This observation indicates that the CO ligands are
more weakly bound to Pt(I) in 1 than to Pt(II) in 2, but
more tightly bound than in the Cu(I), Ag(I), Au(I), and
Rh(I) carbonyl cations which require only brief evacua-
tion to reversibly remove the CO ligands.6 A very slow
reformation of 1 occurs upon reintroduction of CO to a
solution of 2. 1 has been completely characterized by
but high CO pressure is necessary.17 In strong acids, an
olefin is protonated to form a carbocation intermediate,
which isomerizes to a tert-carbocation via the Wagner-
Meerwein rearrangement.18 The protonation of the isomer-
ized olefins is in equilibrium with the deprotonation of
the carbocation.19 Polymerization of the olefins and
carbocations also occurs as a competing reaction in this
system. In the original Koch reaction, the direct reaction
of the carbocations with the dissolved CO in the solution
leads to the formation of acylium cations, which react
with water to give tertiary carboxylic acids. Without
cationic metal carbonyl catalysts, olefins are carbonylated
to form the carboxylic acids in yields as low as 10% under
atmospheric pressure of CO and at room temperature due
to the low CO solubility in the solution and the presence
of the polymerization as a competing reaction.
,8
1
3
195
NMR ( C and Pt), IR, Raman, and EXAFS spectros-
copy.12 The structure of 1 is rigid on the NMR time scale
at room temperature. The strongly polarized, sharp
-
1
Raman band at 165 cm (F ) ca. 0.25) indicates the
presence of a direct Pt-Pt bond. The IR and Raman
spectra in the CO stretching region are entirely consis-
tent with the presence of only terminal CO’s on a
nonbridged Pt-Pt bond with D2d symmetry (see Figure
1
ν
). The average CO stretching vibrational frequency,
-
1
-1
av(CO), for 1 is 2199 cm , higher than 2143 cm , the
1
3
value for free CO. EXAFS measurements show that the
It has been reported that cationic Cu(I), Ag(I), Au(I),
Pd(I), and Rh(I) carbonyl catalysts cause the Koch-type
Pt-Pt bond is 2.718 Å, and the mean length of the Pt-C
bonds is 1.960 Å. The mean Pt-C distance of 1.960 Å is
6
-8
(1.882 Å);1
2 3 2
longer than that found for cis-Pt(CO) (SO F)
1a
reaction to proceed under very mild conditions.
This
paper reveals the first example of the homoleptic, di-
this is consistent with the observation that the CO
ligands are more weakly bound to Pt(I) in 1 than to Pt-
2
+
nuclear, cationic metal carbonyl catalyst, [{Pt(CO)
3 2
} ]
(1), with which olefins readily react with CO to give tert-
(II) in 2 since evacuation of 1 results in the formation of
carboxylic acids in high yields at room temperature and
atmospheric pressure (eq 3). As shown in Table 1, the
addition of the hexacarbonyldiplatinum(I) cation (1)
drastically enhances the rate of carbonylation, which is
completed in 1 h, and tert-carboxylic acids are formed in
high yields. The selectivities of the tert-carboxylic acids
by 1 are similar to those of the cationic Cu(I) or Au(I)
carbonyl catalyst;6 for example, a 2:1 mixture of 2,2-
dimethylpentanoic acid and 2-methyl-2-ethylbutanoic
acid and a 4:2:1 mixture of 2,2-dimethylheptanoic acid,
2
1
through the loss of CO. The geometric optimization for
by a density functional calculation at the B3LYP level
of theory predicts that the dinuclear cation contains two
essentially planar tricarbonyl platinum(I) units that are
linked via a Pt-Pt bond about which they are twisted
by exactly 90.0° with respect to each other (Figure 1).12,14
Hexacar bon yldiplatin u m (I) Cation -Catalyzed Car -
bon yla tion of Olefin s. Platinum catalysts, which work
in both homogeneous and heterogeneous systems, have
assumed a very important position in synthetic chemistry
and the chemical industry.2 For example, platinum(II)
hydrides catalyze the hydroformylation of olefins to
selectively give the straight chain products.2 Platinum
complexes have been employed as active catalysts (Spei-
er’s catalyst) for the hydrosilylation of unsaturated
compounds.1
-8
2
-methyl-2-ethylhexanoic acid and 2-methyl-2-propyl-
,10
pentanoic acid were obtained from 1-hexene and 1-octene,
respectively. The catalytic activity of 1 is close to that of
,15
(16) (a) Green, M.; Spencer, J . L.; Stone, F. G. A.; Tsipis, C. A. J .
Chem. Soc., Dalton Trans. 1977, 1525. (b) Green, M.; Spencer, J . L.;
Stone, F. G. A.; Tsipis, C. A. J . Chem. Soc., Dalton Trans. 1977, 1519.
0,16
(
9
c) Yamamoto, K.; Hayashi, T.; Kumada, M. J . Am. Chem. Soc. 1971,
3, 5301. (d) Sommer, L. H.; Lyons, J . E.; Fujimoto, H. J . Am. Chem.
The Koch reaction, another carbonylation, gives ter-
tiary carboxylic acids in strong acids such as H
2 4
SO , HF,
Soc. 1969, 91, 7051. (e) Chalk, A. J .; Harrod, J . F. J . Am. Chem. Soc.
1965, 87, 16.
H
3
PO , or BF ‚H O, in which no metal catalysts are used
4
3
2
(17) Koch, H. Brennst. Chem. 1955, 36, 321.
(
18) (a) Olah, G. A. Friedel-Crafts and Related Reactions; Wiley-
(
13) Herzberg, G. Spectra of Diatomic Molecules; 2nd ed.; van
Nostrand: New York, 1950.
14) Mogi, K.; Sakai, Y.; Sonoda, T.; Xu, Q.; Souma, Y. J . Mol.
Struct., submitted for publication.
15) Hsu, C. Y.; Orchin, M. J . Am. Chem. Soc. 1975, 97, 3553.
Interscience: New York, 1964. (b) Olah, G. A.; Prakash, G. K. S.;
Sommer, J . Superacids; Wiley-Interscience: New York, 1985.
(19) Olah, G. A. In Stable Carbocation Chemistry; Prakash, G. K.
S.; Schleyer, P. v. R., Eds.; Wiley-Interscience: New York, 1997;
Chapter 1.
(
(

Notes
J . Org. Chem., Vol. 65, No. 23, 2000 8107
the cationic Cu(I) or Au(I) carbonyl catalyst. For example,
the yield of tertiary C7-acids is 73% with the Pt(I)
carbonyl catalyst at the concentration of 0.1 M [{Pt-
and support that the coordination of the substrate to the
metal, i.e., the formation of an olefin-metal-CO inter-
mediate, should be involved in the reaction mechanism
2
+
8
(
CO)
3
}
2
] (1) (2 mmol PtO
2
in 10 mL 96% H
2
SO
4
) and at
for the carbonylation of olefins in strongly acidic media.
1
/1-hexene ) 1.0 mmol/5.0 mmol, being slightly lower
A theoretical study (B3LYP level of theory) on the copper-
(I), silver(I), and gold(I) carbonyl cation-catalyzed carbo-
nylations has indicated that the carbonylations of eth-
ylene, propylene, and isobutene prefer to proceed via
than the 80% yield with the Au(I) carbonyl catalyst at
the same concentration of 0.1 M Au and at the same
+
+
8c
ratio of Au /1-hexene ) 1.0 mmol/5.0 mmol. For com-
parison, the yield of the tertiary C7-acids is 80% with
the Cu(I) carbonyl catalyst at the concentration of 0.4 M
Cu and at Cu /1-hexene ) 1.0 mmol/5.0 mmol. When
the concentration of 1 is kept at 0.1 M, the increase in
the added substrate, 1-hexene, from 1/1-hexene ) 1.0
mmol/5.0 mmol to 1.0 mmol/10.0 mmol does not result
in a significant change in the yield of the tertiary C7-
acids, whereas the decrease in the concentration of 1 from
2
2
olefin-metal(I)-dicarbonyl intermediates. For cis-Pt-
2
+
(CO)
2
(solv) (2), the Pt-CO bonding to Pt(II) is so strong
+
+
7c
that it is difficult for the substrate to replace a CO ligand
to form the olefin-Pt(II)-carbonyl intermediate, and
therefore, 2 was observed to have a very low catalytic
activity for the carbonylation of olefins in strong acids.
Con clu sion s
0
2 4
.1 to 0.05 M in 96% H SO leads to the decrease in the
In summary, we have found that hexacarbonyldiplati-
yield of the tertiary C7-acids from 73% to 62% due to the
presence of polymerization as a competing reaction. In
contrast to the high catalytic activity of 1, cis-Pt-
2+
num(I), [{Pt(CO)
3
}
2
]
(1), the first homoleptic, dinuclear,
cationic platinum carbonyl complex, is formed in concd
SO solution under a CO atmosphere. The Pt-C
bonding in [{Pt(CO)
H
2
4
2
+
(CO)
2
(solv) (2) was found to have a very low catalytic
2+
3
}
2
]
is much weaker than in cis-Pt-
]2+ is the first example of the
3 2
(solv). [{Pt(CO) }
activity for the carbonylation of olefins, with which
tertiary C7-acids were obtained from 1-hexene in a total
yield as low as 20% in 96% H
2+
(
CO)
2
homoleptic, dinuclear, cationic metal carbonyl catalyst,
which, in concd H SO solution, catalyzes the carbony-
2 4
SO at room temperature
2
4
and atmospheric CO pressure.
lation of olefins to give tert-carboxylic acids in high yields
at room temperature and 1 atm of CO, whereas cis-Pt-
2
+
(
CO)
2
(solv) has a very low catalytic activity.
Exp er im en ta l Section
Commercial reagents, PtO
Pure Chemicals), H SO (96%, Kanto Chemical Co.), CO (Nippon
Sanso), D SO
(96%, CIL), and 13CO ( C enrichment 99%, ICON)
were used for the preparation and characterization of the new
2
‚xH
2
O (Pt, 78.8 wt %; Mitsuwa
Recently, Mogi et al. calculated the average dissocia-
2
+
2
4
tion energy for [{Pt(CO)
3
}
2
]
(as one-quarter of the
13
2
4
2
+
reaction energy for the dissociation of [{Pt(CO)
3
}
2
14
]
(D2d)
2
+
to [Pt
2
(CO)
2
]
(D2h, linear)) to be 60.4 kcal/mol. On the
2+
2
platinum(I) carbonyl catalyst, [{Pt(CO)
(CO) ] (solv) (2). Reagents (special grade, Wako Pure Chemical)
3
}
]
(1), and cis-[Pt-
2
0
2+
2
other hand, Armentrout and co-workers determined the
+
1-pentene, 1-hexene, 1-octene, 1-decene, and cyclohexene were
used for the carbonylation without further purification. The
preparation and characterization of 1 and 2 were carried out as
previously described.12 The carbonylation of the olefins was
carried out by a method similar to that described in previous
bond energies for the gas-phase complexes (CO)M -CO
to be 41 and 26 kcal/mol for M ) Cu and Ag, respectively,
2
1
and Veldkamp and Frenking calculated (MP2 level of
+
theory) the (CO)M -CO bond energies to be 27 and 50
kcal/mol for M ) Ag and Au, respectively. These results
papers.
concd H
8
Using a syringe, an olefin was added dropwise into the
SO solution of 1. After the reaction was finished, the
predicted the stability of the monovalent, metal carbonyl
2
4
+
+
reaction mixture was poured over ice-water. The products were
extracted with n-hexane and analyzed by GC, NMR, and IR.
Identification of the products in Table 1 was carried out by a
comparison of the retention times and “spiking” with the
authentic samples prepared by the Cu(I) carbonyl cation-
catalyzed carbonylation of olefins.
cations to be in the order of [Ag(CO)
2
] < [Cu(CO)
. The prediction is in good
agreement with the experimental observations that to
2
] <
+
2+
[
Au(CO)
2
]
3 2
< [{Pt(CO) } ]
2
+
remove CO ligands from [{Pt(CO)
3
}
2
]
requires a pro-
longed evacuation (ca. 1 day) of the solution of 1 whereas
+
+
+
[
2 2 2
Cu(CO) ] , [Ag(CO) ] , and [Au(CO) ] require only a
Ack n ow led gm en t. We thank Profs. B. T. Heaton,
K. Kanamori, and T. Eguchi and Drs. C. J acob, K. Mogi,
and Y. Ichihashi for their valuable help and discussions.
Profs. H. Willner and F. Aubke are acknowledged for a
preprint of their work prior to publication. Q.X. ex-
presses his thanks to the Society of Synthetic Organic
Chemistry, J apan, for Daicel Award 1997/1998 and to
Daicel Chemical Industries, LTD for financial support.
brief evacuation (several seconds) to reversibly remove
the CO ligands.6,8 As shown in Table 1, the conversions
of olefins to tertiary carboxylic acids by the platinum(I)
carbonyl catalyst are comparable to those by the Cu(I),
Ag(I), and Au(I) carbonyl catalysts, despite the signifi-
cantly high stability of the Pt-CO bonds in the dinuclear
Pt(I) carbonyl complex. The observations of the Pt(I)
carbonyl catalyst conflict with the CO carrier model2
a,7c
J O000883C
(
20) Meyer, F.; Chen, Y.-M.; Armentrout, P. B. J . Am. Chem. Soc.
995, 117, 4071.
21) Veldkamp, A.; Frenking, G. Organometallics 1993, 12, 4613.
1
(22) Mogi, K.; Sonoda, T.; Sakai, Y.; Xu, Q.; Souma, Y., to be
submitted for publication.
(