High-yielding tandem hydroformylation/hydrogenation of a terminal olefin to produce a linear alcohol using a Rh/Ru dual catalyst system

Article abstract of DOI:10.1002/anie.201001327

(Chemical equation presented) A dual catalyst system has been developed for tandem hydroformylation/hydrogenation to produce n-undecanol from 1-decene in one pot. A combination of xantphos/[Rh(acac)(CO)₂] and Shvo's catalyst (1) afforded the best results (see scheme; acac = acetylacetonate, DMA = N,N-dimethylacetamide). Polar solvents effectively suppressed the formation of undecyl formate.

Full text of DOI:10.1002/anie.201001327

Communications
DOI: 10.1002/anie.201001327
Alcohol Synthesis
High-Yielding Tandem Hydroformylation/Hydrogenation of a
Terminal Olefin to Produce a Linear Alcohol Using a Rh/Ru Dual
Catalyst System**
Kohei Takahashi, Makoto Yamashita, Takeo Ichihara, Koji Nakano, and Kyoko Nozaki*
Linear 1-alkanols (n-alcohols) are widely used in industry as
precursors of detergents and plasticizers.[1] Direct and selec-
tive conversion of a terminal olefin into an n-alcohol by
regioselective hydration is considered an ideal process, and it
is referred to as one of the “ten challenges for catalysis”.[2] In
reality, current industrial production of n-alcohols mostly
employs a two-step process consisting of hydroformylation of
terminal olefins, purification of n-aldehydes, and then hydro-
genation of n-aldehydes to n-alcohols. A one-pot tandem
hydroformylation/hydrogenation reaction would be an attrac-
tive alternative for n-alcohol production.[3] A one-pot process
would be advantageous over the two-step process in the
following way: 1) a one-pot process simplifies the process
operation, and 2) syngas (a mixture of H2 and CO) can be
directly used for hydrogenation instead of using hydrogen
purified from syngas via membrane separation.[4] Therefore,
there have been many reports on the tandem hydroformyla-
tion/hydrogenation for direct synthesis of alcohols with
alkylphosphine ligands using metal catalysts, such as Co,[5]
Rh,[6] Ru,[7] and Pd,[8]. Although these tandem systems gave a
mixture of n- and i-alcohols in good yields (mostly > 90%), a
significant amount of alkane was often given. The most
problematic issue is the low normal/iso selectivities (n/i < 8) in
the hydroformylation step, causing a low n-alcohol yield (up
to 81%). Recently, a supramolecular catalyst system contain-
ing Rh and an acyl guanidine-tethered triphenylphosphine
ligand was reported as an effective catalyst for the one-pot
conversion of olefins into the corresponding homologated
linear alcohols in up to 72% yield.[9] Earlier this year a Cole-
Hamilton and co-workers proposed a new strategy wherein
two ligands were mixed for Rh-catalyzed hydroformylation/
hydrogenation in a one-pot process to provide linear alcohols
in up to 87% yield.[6f] While these systems depend on one
single metal catalyst to perform the two different reactions,
we became interested in the admixture of two catalysts, each
of which operates one reaction with high efficiency without
disturbing the other reaction.[10] Herein, we report a high-
yielding synthesis of n-alcohol (> 90%) by the reaction of a
terminal olefin with syngas using Rh/xantphos[11] and Shvoꢀs
catalyst[12] together in one pot.
For the linear-selective hydroformylation, we selected an
Rh/xantphos catalyst.[11] Xantphos is known to provide the
excellent levels of linear selectivity in hydroformylation of
terminal olefins and is a triarylphosphine ligand, which is
stable in the presence of the generated alcohols. For
aldehyde-selective hydrogenation over the coexisting olefins,
we selected a ruthenium-based ligand–metal bifunctional
catalysts. Such a catalyst converts dihydrogen into two
nonequivalent hydrogen atoms; one is protic and the other
is hydridic.[13] Both of the hydrogen atoms simultaneously
interact with a substrate via a polar transition state in an
outer-sphere mechanism. As a result, the hydrogenation of a
=
polar double bond predominates over that of a C C bond.
Among the Ru catalysts we examined, the use of Shvoꢀs
complex 1 gave the best result. Details of the Ru catalysts
screening are summarized in Table 1. Under an atmosphere of
H2/CO (1/1, 2.0 MPa), 1-decene was heated at 1608C for
1 hour in the presence of Ru catalysts 1–5 and Rh/xantphos.
By using Shvoꢀs complex 1, 1-undecanol (n-alcohol) was
obtained in 84.9% yield (entry 1). For other Ru catalysts we
examined, the use of additional base was required. When Ru
complex 2 bearing an amino-Cp ring[14] or a mixture of Cp*Ru
complex 3 and Ph2PCH2CH2NH2 (6)[15] was used, the for-
mation of byproducts became problematic because of the
slow hydrogenation of aldehydes (entries 2 and 3). Significant
isomerization of 1-decene into internal olefins were detected
with (p-cymene)Ru catalyst 4 (entry 4)[16] or with hexacoor-
dinate RuCl2 complex 5[17] (entry 5).
[*] K. Takahashi, Dr. M. Yamashita, T. Ichihara, Dr. K. Nakano,
Prof. Dr. K. Nozaki
Department of Chemistry and Biotechnology
Graduate School of Engineering, The University of Tokyo
7-3-1 Hongo, Bunkyo-ku 113-8656, Tokyo (Japan)
Fax: (+81)3-5841-7263
E-mail: nozaki@chembio.t.u-tokyo.ac.jp
Homepage: http://park.itc.u-tokyo.ac.jp/nozakilab/
After optimization of the reaction conditions, the yield of
n-alcohol was elevated up to 90.1%, which is the highest
among reported values to date for the one-pot process. A
significant solvent effect on the yield was detected. The use of
less-polar aprotic solvents such as toluene and THF resulted
in the lower yields of n-alcohol with an increase of dodecyl
formate (compare entry 1 with entries 6 and 7). In contrast, a
slight improvement in the yield was achieved in polar aprotic
solvents with a suppression of dodecyl formate (entries 8 and
[**] This work was supported by KAKENHI (grant nos. 21245023 and
21685006) from MEXT (Japan).
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201001327.
4488
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Chemie
Table 1: Catalyst optimization.[a]
1–5 showed catalytic activity in the
coexistence of CO, although the
catalytic activity was lower than
the originally reported values
under pure H2. The deceleration of
hydrogenation may be attributed to
the reversible ligation of either CO
or xantphos to the Ru catalyst,
which lowers the concentration of
the active Ru species available for
hydrogenation.
The following features were fur-
ther elucidated by control experi-
ments described in the Supporting
Information. Formation of decane
could be attributed to the direct
hydrogenation of 1-decene by both
Rh and Ru hydride species.[19] The
Ru catalyst is responsible for the
olefin isomerization because the
isomerization product increased at
a higher Ru/Rh ratio. Undecyl for-
mate formed by insertion of CO
into RuOC11H23 bond of the alk-
oxide intermediate during the
hydrogenation of the aldehyde by 1.
In conclusion, a new dual cata-
lyst system—a combination of xant-
phos/[Rh(acac)(CO)2] and Shvoꢀs
Entry
Ru cat.
Solvent T [8C]
t [h]
Conv. [%]
Yield [%][b]
B (n/i)
A (n/i)
C
D
1
1
iPrOH
iPrOH
iPrOH
iPrOH
iPrOH
toluene
THF
DMF
DMA
DMA
160
160
160
160
160
160
160
160
160
80
1
1
1
1
1
1
1
1
1
100
100
100
100
100
100
100
100
100
52.1
100
100
100
84.9 (17)
63.5 (23)
37.0 (19)
5.4 (–)
59.1 (37)
80.1 (20)
63.5 (14)
88.2 (22)
89.6 (22)
24.5 (>50)
89.3 (36)
49.7 (35)
90.1 (22)
0.9 (2)
14.0 (9)
41.0 (0)
64.0 (13)
7.2 (12)
2.7 (8)
4.3 (7)
0.6 (1)
1.0 (2)
16.7 (>50)
1.5 (4)
1.7
2.5
2.7
26.0
11.0
3.2
8.6
3.8
4.9
4.0
1.2
2[c]
3[e]
4[f]
5[g]
6
2[d]
3.3
2.0
0.4
0.5
9.6
11.0
3.5
1.2
0.0
0.3
0.3
1.1
3+6[d]
4[d]
5[d]
1
7
8
9
10
11
12
13
1
1
1
1
1
1
1
1
48
1
DMA
80
2.0
5.4
1.9
DMA
DMA
120
120
34.3 (41)
1.0 (1)
12.5
[a] Reaction condition: Ru complex (2.5 mol% of Ru), Rh complex (1 mol%), xantphos (2 mol%),
solvent (4 mL). [b] Yields were determined by GC analysis using dodecane as an internal standard after
correction for purity of the substrate (96.7% 1-decene + 1.0% decane + 2.3% internal olefins, mainly
(Z)- and (E)-2-decene), [1-decene]/[dodecane]=2. All values are an average of two independent
reactions. Byproducts lower than 4% yield are omitted from this table. Details are reported in the
Supporting Information. [c] 4.7% of acetal was detected. [d] tBuOK (1 mol%) was added. [e] 4.3% of
aldol adduct was detected. [f] The yield of obtained i-alcohol was too low to determine the n/i ratio.
[g] 6.4% of acetal was detected. acac=acetylacetonate, DMA=N,N-dimethylacetamide, DMF=N,N-
dimethylformamide, THF=tetrahydrofuran, Ts=4-toluenesulfonyl.
catalyst—has
accomplished
a
highly efficient production of
n-alcohol by a simple one-pot pro-
cess utilizing syngas for hydrogena-
tion. Under the best conditions,
1-undecanol was produced from
1-decene in 90.1% yield, which is
9). Reaction temperature was also essential for the product
distribution. At 808C, both hydroformylation and hydro-
genation steps were very slow (entries 10 and 11).[11] At 1208C
in 1 hour, 1-decene was completely consumed but the main
product was the aldehyde with a high n/i ratio (entry 12).
Finally, prolonged reaction time at 1208C gave n-alcohol in
90.1% yield (entry 13).
Scheme 1. Expected species in the present tandem catalyst system.
Although the active species for catalysis is not yet fully
characterized, the following studies suggest that the hydro-
formylation is catalyzed by Rh/xantphos and the hydro-
genation is operated by Ru catalyst 1 with/without xantphos.
When an admixture of [Rh(acac)(CO)2], xantphos, and
complex 1 in a ratio of 1:2:2.5 was heated at 1208C for
15 minutes under a syngas atmosphere, several phosphorus-
containing species were detected including [(xant-
phos)Rh(H)(CO)2] (7), [ (k1-xantphos)Ru(Cp’)(CO)2] (8)
(Cp’ = tetraphenylcyclopentadienone), free xantphos, and
other minor species (Scheme 1).[18] Considering that all
examples offered high n/i ratios (> 15) of the resulting
alcohols, the step responsible for the high linear selectivity
is hydroformylation catalyzed by 7.[11] Notably, all catalysts
the highest yield to date. The best yield achieved with 1 is a
result of the following factors: 1) the highest hydrogenation
activity of 1 under CO, 2) well-suited Rh/L/Ru ratio, 3) the
absence of any additional base, and 4) the best solvent
(DMA).
Experimental Section
Standard procedure of tandem hydroformylation/hydrogenation.
[Rh(acac)(CO)2] (5.2 mg, 20 mmol), xantphos (23.1 mg, 40.0 mmol),
and DMA (1.0 mL) were added to a 50 mL stainless autoclave under
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Communications
an argon atmosphere. The autoclave was flushed with H2/CO (1/1)
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1 in DMA (25 mmol, 50 mmol of Ru, 3.0 mL) was added to the
reaction mixture followed by a mixture of substrate 1-decene and
dodecane ([1-decene]/[dodecane] = 2.00; 550 mL, ca. 450 mg,
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