1540
J . Org. Chem. 2000, 65, 1540-1543
Notes
under an atmospheric pressure of CO.6-8 [Pt(CO4)]-
[Sb2F11 has recently been used for the stereospecific
A New Rh od iu m Ca ta lyst: F or m a tion of
[Rh (CO)4]+ in Con cen tr a ted Su lfu r ic Acid
a n d Its Ap p lica tion to Ca r bon yla tion of
Olefin s
]
2
tetramerization of 2-propynol and the polymerization of
arylacetylenes.9
Rhodium catalysts, most of which work in organic
solvents, have been employed in many important reac-
tions, such as the hydrogenation,10 hydroformylation, and
carbonylation of unsaturated compounds.1 In this paper,
we report a new rhodium carbonyl catalyst in concd
H2SO4, with which olefins react with CO to produce
tertiary carboxylic acids in high yields at atmospheric
pressure and room temperature. This work extends the
family of the cationic metal carbonyl catalysts for car-
bonylation of olefins from groups 11 and 10 to the group
9 elements.
Qiang Xu,* Hisako Nakatani, and Yoshie Souma
Osaka National Research Institute, AIST, MITI, 1-8-31,
Midorigaoka, Ikeda, Osaka, 563-8577, J apan
Received October 21, 1999
In tr od u ction
Metal carbonyls have played a very important role in
chemistry and the chemical industry.1 For the typical
metal carbonyls such as Ni(CO)4, Co2(CO)8, Fe(CO)5, and
Mn(CO)43-, the average vibrational frequencies, ν(CO),
are considerably lower than the value for free CO, 2143
cm-1, mainly due to the metal-to-CO π-back-bonding.2
Reactions catalyzed by such metal carbonyls usually
require drastic conditions; for example, the Roelen and
Reppe reactions, which employ Co2(CO)8 or Ni(CO)4 to
catalyze the carbonylation of olefins to produce aldehydes
and alkanoic acids, are operated at high temperature and
high pressure.1
In the last ca. 10 years, there has been a rapid
development in the preparation and structural charac-
terization of homoleptic metal carbonyl cations and their
cationic derivatives; this new class of metal carbonyl
complexes ranges from group 6 to group 12.3-5 In contrast
to the typical metal carbonyl complexes, the new family
of metal carbonyls has a distinguishing characteristic in
that the CO vibrational frequencies are considerably
raised; they have remarkably reduced π-back-bonding
and reactive CO ligands. There have been reports on the
use of the metal carbonyl cations as catalysts under mild
conditions. Cu(I), Ag(I), Au(I), and Pd(I) carbonyls have
been shown to be highly active for the catalytic carbo-
nylation of olefins (the Koch-type reaction) in strong acids
Resu lts a n d Discu ssion
F or m a tion of Rh od iu m (I) Tetr a ca r bon yl Ca tion ,
[R h (CO)4]+, in Con cen t r a t ed H2SO4. Very recently,
new Rh(I) and Rh(III) carbonyl cations have been gener-
ated. The rhodium(I) tetracarbonyl cation, [Rh(CO)4]+,
was prepared by the solvolysis and carbonylation of
[Rh(µ-Cl)(CO)2]2 in HSO3F11 and isolated by treating
[Rh(µ-Cl)(CO)2]2 with Ag[1-Et-CB11F11];12 in both of the
cases, Rh retains the oxidation state of +1. [Rh(CO)4]+
was also prepared by the reductive carbonylation of
Rh(SO3F)3 in HSO3F.11 The Rh(III) tricarbonyl com-
plex, Rh(CO)3(SO3F)3, was formed by the oxidation of
[Rh(CO)4]+ with S2O6F2, one of the strongest oxidizers,
in HSO3F.11
We have found a remarkably facile route for the
synthesis of [Rh(CO)4]+ in strong acids. By dissolving Rh4-
(CO)12 in concd H2SO4 under a CO atmosphere at room
temperature, a yellow-brown solution was formed, which
exhibits no 1H NMR resonance for a hydride and no
Raman band due to ν(Rh-Rh), in contrast with the
observation of a resonance at -20 ppm for the hy-
dride13 and two Raman bands at 199 and 163 cm-1 due
to ν(Ir-Ir) for [Ir4(CO)12H2]2+ formed by the dissolution
of Ir4(CO)12 in concd H2SO4. During the reaction, the CO
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10.1021/jo991659u CCC: $19.00 © 2000 American Chemical Society
Published on Web 02/08/2000