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Angewandte
Communications
Iridium Catalysis
Hot Paper
The Retro-Hydroformylation Reaction**
Shuhei Kusumoto, Toshiumi Tatsuki, and Kyoko Nozaki*
Abstract: Hydroformylation, a reaction that adds carbon
monoxide and dihydrogen across an unsaturated carbon–
carbon multiple bond, has been widely employed in the
chemical industry since its discovery in 1938. In contrast, the
reverse reaction, retro-hydroformylation, has seldom been
studied. The retro-hydroformylation reaction of an aldehyde
into an alkene and synthesis gas (a mixture of carbon
monoxide and dihydrogen) in the presence of a cyclopenta-
dienyl iridium catalyst is now reported. Aliphatic aldehydes
were converted into the corresponding alkenes in up to 91%
yield with concomitant release of carbon monoxide and
dihydrogen. Mechanistic control experiments indicated that
the reaction proceeds by retro-hydroformylation and not by
a sequential decarbonylation–dehydrogenation or dehydro-
genation–decarbonylation process.
ric reactions mediated by ruthenium or rhodium complexes[5]
and iron porphyrin complexes,[6,7] transformations of steroidal
aldehydes catalyzed by heterogeneous rhodium or palladium
catalysts,[8] and side reactions in decarbonylation reactions
catalyzed by rhodium or iridium complexes.[9,10] Some related
reactions, such as a catalytic transfer of a formyl group from
1-heptanal to cyclohexene with a ruthenium complex[11] and
the migration of a formyl group to isomerize a linear aldehyde
into its branched isomer with a rhodium catalyst[12] have also
been reported. We envisioned that the efficient elimination of
synthesis gas from the reaction system would enable the
formation of alkenes from aldehydes without any formyl-
group acceptors if appropriate catalysts were applied. Earlier
this year, while our studies were in progress, Dong and co-
workers reported a transfer hydroformylation reaction cata-
lyzed by a rhodium/Xantphos system for the conversion of
aliphatic aldehydes into the corresponding alkenes by trans-
ferring a hydrogen atom and a formyl group to a strained
alkene.[13] In this process, the key for the reaction to proceed
was proposed to be the use of strained alkenes, such as
norbornadiene, as effective hydrogen and formyl-group
acceptors (Scheme 2). However, a retro-hydroformylation
F
or more than 75 years since its discovery, hydroformyla-
tion, that is, the addition of carbon monoxide and dihydrogen
to an unsaturated carbon–carbon multiple bond, has been
widely employed in the chemical industry for the synthesis of
aliphatic aldehydes from olefins.[1] Thus, among the reactions
that utilize synthesis gas (a mixture of carbon monoxide and
dihydrogen), such as the Fischer–Tropsch process,[2] methanol
synthesis,[3] and others,[4] hydroformylation has long been
a subject of most intensive studies both from industry and
academia. On the other hand, the reverse reaction, retro-
hydroformylation, has rarely been studied thus far
(Scheme 1). The examples have been limited to stoichiomet-
Scheme 2. Transfer hydroformylation.
reaction, that is, the conversion of an aldehyde into an alkene
with concomitant release of carbon monoxide and dihydro-
gen, has previously not been reported. Herein, we report the
first retro-hydroformylation reaction, an acceptor-free dehy-
droformylation process that is catalyzed by cyclopentadienyl
iridium complexes.
The retro-hydroformylation of cyclododecanecarbalde-
hyde was accomplished in up to 91% yield with cyclo-
pentadienyl iridium complexes C–F. Representative results of
the optimization of the catalyst and the reaction conditions
are summarized in Table 1. In all reactions, cyclododecane-
carbaldehyde (0.50 mmol) was treated with 10 mmol of
a catalyst at 1608C (except for entries 12–14) in an open
glass tube for 20 hours, and then the reaction mixture was
Scheme 1. Hydroformylation and retro-hydroformylation.
[*] Dr. S. Kusumoto, T. Tatsuki, Prof. Dr. K. Nozaki
Department of Chemistry and Biotechnology
Graduate School of Engineering, The University of Tokyo
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)
E-mail: nozaki@chembio.t.u-tokyo.ac.jp
[**] We are grateful to Prof. Clark Landis (Univ. of Wisconsin, Madison)
for valuable comments. A part of this work was conducted in the
Research Hub for Advanced Nano Characterization, The University
of Tokyo, supported by the Ministry of Education, Culture, Sports,
Science and Technology (MEXT; Japan). This work was partly
supported by a Takasago International Corporation Award in
Organic Synthetic Chemistry (Japan) and a Sasakawa Scientific
Research Grant from The Japan Science Society.
1
analyzed by GC and H NMR spectroscopy. The three main
products were the retro-hydroformylation product cyclo-
dodecene (1), the decarbonylation product cyclododecane
(2), and cyclododecylmethanol (3), which results from hydro-
genation of the starting aldehyde. First, the indispensability of
the metal catalysts was confirmed by a control reaction
without any catalyst (entry 1).[14] Rhodium complex A, which
was used for the transfer hydroformylation reported by Dong
Supporting information for this article is available on the WWW
8458
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2015, 54, 8458 –8461