Tandem isomerization/hydroformylation/hydrogenation of internal alkenes to n-alcohols using Rh/Ru dual-or ternary-catalyst systems

Article abstract of DOI:10.1021/ja407523j

A one-pot three-step reaction, isomerization/hydroformylation/hydrogenation of internal alkenes to n-alcohols, was accomplished by employing a Rh/Ru dual-catalyst system. By using a combination of Rh(acac)(CO)₂/ bisphosphite and Shvo's catalyst, (Z)-2-tridecene was converted to 1-tetradecanol in 83% yield with high normal/iso selectivity (n/i = 12). The method was applicable to other internal alkenes, including functionalized alkenes, such as an alkenol and an alkenoate. Furthermore, addition of a third component, Ru₃(CO)₁₂, effectively improved the n/i ratio in the tandem isomerization/hydroformylation/hydrogenation of methyl oleate (from n/i = 1.9 to 4.4). Control experiments revealed that the isomerization was mediated by both Rh and Ru and that the coexistence of Rh and Ru was essential for hydrogenation of aldehyde under H₂/CO.

Full text of DOI:10.1021/ja407523j

Article
pubs.acs.org/JACS
Tandem Isomerization/Hydroformylation/Hydrogenation of Internal
Alkenes to n‑Alcohols Using Rh/Ru Dual- or Ternary-Catalyst Systems
Yamato Yuki,† Kohei Takahashi,† Yoshiyuki Tanaka,‡ and Kyoko Nozaki*,†
†Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku,
Tokyo 113-8656, Japan
‡Mizushima R&D Center, Mitsubishi Chemical Corporation, 3-10 Ushiodori, Kurashiki, Okayama 712-8054, Japan
S
* Supporting Information
ABSTRACT: A one-pot three-step reaction, isomerization/
hydroformylation/hydrogenation of internal alkenes to n-
alcohols, was accomplished by employing a Rh/Ru dual-catalyst
system. By using a combination of Rh(acac)(CO)2/bisphosphite
and Shvo’s catalyst, (Z)-2-tridecene was converted to 1-
tetradecanol in 83% yield with high normal/iso selectivity (n/i
= 12). The method was applicable to other internal alkenes,
including functionalized alkenes, such as an alkenol and an
alkenoate. Furthermore, addition of a third component,
Ru3(CO)12, effectively improved the n/i ratio in the tandem
isomerization/hydroformylation/hydrogenation of methyl oleate (from n/i = 1.9 to 4.4). Control experiments revealed that the
isomerization was mediated by both Rh and Ru and that the coexistence of Rh and Ru was essential for hydrogenation of
aldehyde under H2/CO.
system, which afforded n-undecanol in 90% yield with n/i = 22
from 1-decene.2i,j
INTRODUCTION
■
Combination of multiple catalysts in a single vessel to promote
multistep conversion of substrates has become widely used in
homogeneous catalysis.1 The tandem hydroformylation/hydro-
genation of terminal alkenes (1-alkenes) to n-alcohols (1-
alkanols) is one of the major research targets of the
multicatalyst systems: namely, both the n-selective hydro-
formylation and the subsequent hydrogenation of the resulting
n-aldehyde by syngas (a mixture of H2 and CO) in one pot.2 It
would be even more desirable if a mixture of terminal and
internal alkenes in a refinery mixture could be directly applied
to the n-alcohol synthesis.3 Thus, a tandem three-step reaction
consists of the isomerization from internal to terminal alkenes,
the n-selective hydroformylation, and the aldehyde hydro-
genation is an attractive avenue for n-alcohol synthesis.
For the first two steps (Scheme 1, reaction A + B), the
isomerization/hydroformylation of internal alkenes to normal
aldehydes has been well studied since th e1980s. High n/i ratios
(the ratio of normal product to iso product) up to 24 were
reported by the researchers of UCC for the hydroformylation
of 2-butene to pentanal using a Rh complex of bulky
bisphosphite.4 Since then, continuous efforts have been made
to improve the two-step reaction by the development of
bidentate phosphorus ligands5 such as phosphacyclic ligands,5a
pyrrolyl ligands,5g etc.
For the three-step one-pot conversion of internal alkene to n-
alcohol (Scheme 1, reaction A + B + C), the cobalt
trialkylphosphine catalyst developed by Shell Oil Co. is a
well-established system.6 The current state of the art for the
selectivity to alcohols is up to 90% and the n/i ratio is up to 9
with high catalytic activity for a mixture of internal decenes.6c
This process is also efficient in terms of easy catalyst separation
and low cost of catalytic components. The process is
industrially operated on a large scale and is the most preferred
method to obtain linear aliphatic alcohols (>C5). Few other
examples have been reported, but the n/i ratios are insufficient
(n/i up to 5.3).2k−o Here we report a highly n-selective three-
step one-pot reaction, isomerization/hydroformylation/hydro-
genation to produce n-alcohols from various internal alkenes
using a Rh/bisphosphite/Ru dual-catalyst system, where Rh
and Ru cooperatively work in both the isomerization and
hydrogenation steps. Furthermore, addition of a third catalyst
accelerated the isomerization process further to yield alcohols
in a higher n/i ratio when methyl oleate was employed as a
substrate.
RESULTS AND DISCUSSION
■
Isomerization/Hydroformylation/Hydrogenation of
(Z)-2-Decene and (Z)-2-Tridecene Catalyzed by Rh/
Phosphorus Ligands/Shvo’s Catalyst System. First, the
For the last two steps (Scheme 1, reaction B + C), that is the
tandem normal-selective hydroformylation/hydrogenation of
terminal alkenes to n-alcohols, Co and Rh systems modified by
a trialkylphosphine were reported to be effective.2a−d
Previously, we reported a Rh/bisphosphine/Ru dual-catalyst
Received: July 22, 2013
Published: November 5, 2013
© 2013 American Chemical Society
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Scheme 1. One-Pot Isomerization/Hydroformylation/Hydrogenation of Internal Alkene to Normal Alcohol
Table 1. Isomerization/Hydroformylation/Hydrogenation of Internal Alkenes Catalyzed by Rh/Phosphorus Ligand/Shvo’s
a
Catalyst
alcohol yield
(%)
aldehyde yield
(%)
direct
time
(h)
conversn
(%)
total
b
hydrogenation
of CC (%)
total others
c
d
e
run
alkene
ligand
n/i
n
i
n
i
(%)
f
1
(Z)-2-decene
(Z)-2-decene
(Z)-2-decene
(Z)-2-decene
(Z)-2-decene
(Z)-2-tridecene
1-octene
PPh3 (4.0 mol %)
P(OPh)3 (4.0 mol %)
XANTPHOS
BISBI
36
36
36
36
36
36
18
18
18
18
36
36
47
0.8
0.7
1.3
0.4
18
12
40
27
17
16
4.8
24
8.1
38
11
13
nd
1.0
0.4
f
2
94
8.0
6.5
nd
f
3
88
35
27
4.0
2.4
nd
5.7
4
42
6.0
75
19
2.6
4.0
6.0
4.8
6.7
5.5
5.7
5.0
4.4
trace
trace
trace
2.6
5
A4N3
99
4.2
7.1
0.6
1.5
2.3
3.0
19
3.5
0.2
6
A4N3
100
100
100
100
100
83
trace
59
trace
1.5
7
A4N3
24
4.4
8
(Z)-2-octene
(E)-2-octene
(E)-4-octene
A4N3
34
49
1.5
1.7
9
A4N3
45
16
1.2
6.4
10
11
12
A4N3
46
17
0.9
8.2
e
1-methylcyclohexene A4N3
37
trace
trace
trace
trace
trace
6.3
g
g
e
2-methylstyrene
(E:Z = 1.8:1.0)
A4N3
100
4.9
69
14
6.6
7.7
g
h
e
13
14
(Z)-6-nonen-1-ol
A4N3
A4N3
36
36
100
9.3
4.6
62
6.7
14
trace
trace
trace
trace
24
5.0
12
g
g
e
(Z)-6-nonenyl
acetate
100
65
6.6
g
h
g
g
g
i
j
15
methyl oleate
(Z)-2-decene
methyl oleate
A4N3
A4N3
A4N3
36
36
36
86
1.9
23
37
19
5.0
3.0
23
nd
k
16
k
100
93
71
3.1
1.0
trace
trace
7.7
3.7
h
g
i
j
17
4.4
53
12
trace
29
nd
a
Conditions: alkene 2.0 mmol, H2 0.25 MPa, CO 0.25 MPa, Rh(acac)(CO)2 1.0 mol %, ligand 2.0 mol %, Shvo’s catalyst 1.5 mol % (based on Ru
atom), 1,4-dioxane 4.0 mL, 120 °C. Conversion is defined as consumption of the CC bond. Yields were determined by gas chromatography using
b
dodecane or tridecane as an internal standard unless otherwise mentioned. Total n/i = ((yield of n-alcohol) + (yield of n-aldehyde))/((yield of i-
c
d
alcohols) + (yield of i-aldehydes)). Total yield of i-alcohols estimated by GC by comparing the peak area with that of n-alcohol. Total yield of i-
e
aldehydes estimated by GC by comparing the peak area with that of n-aldehyde. Yields were estimated by GC by comparing the peak area with that
of n-alcohol. Could not be determined because of the overlapping of the peak with those of isomerized alkenes. Determined by H NMR using
1,3,5-trimethoxybenzene or 1,1,2,2-tetrachloroethane as internal standard. Isolated yield by silica gel column chromatography. NMR yield after
rough separation by silica gel column chromatography. Minor uncharacterized signals were found in the H NMR spectrum of the crude mixture.
f
g
1
h
i
j
1
k
Ru3(CO)12 1.5 mol % (based on Ru atom) was added as an extra catalyst.
reaction of (Z)-2-decene with syngas was examined in the
presence of Rh(acac)(CO)2, Shvo’s catalyst,7 and various
phosphorus ligands (runs 1−5 of Table 1 and Figure 1). The
use of PPh3 resulted in a low conversion of (Z)-2-decene to n-
alcohol with a low n/i ratio (4.8%, total n/i of alcohol and
aldehyde was 0.8, run 1). With P(OPh)3, the conversion of
alkene was improved but the n/i ratio remained low (24% n-
alcohol yield, n/i = 0.7, run 2). Both the yield of n-alcohol and
the n/i ratio stayed low with bisphosphines XANTPHOS8
(35%, n/i = 1.3, run 3) and BISBI9 (6.0%, n/i = 0.4, run 4),
which are known to be effective for n-selective hydro-
formylation of terminal alkenes. In sharp contrast, a significant
increase of n-alcohol yield and n/i was observed with the bulky
bisphosphite ligand A4N310 (75%, n/i = 18, run 5). These
trends well reflect the fact that the Rh/bisphosphite system is
generally more effective for the conventional two-step reaction,
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reaction rate from the n-aldehyde, nonanal, to the n-alcohol, 1-
nonanol. One possible explanation of the phenomenon is the
inhibition of hydrogenation by alkenes. Terminal or (Z)-
alkenes may more preferably coordinate to the Ru because of
their smaller steric repulsion with the other ligands on the Ru,
and that interferes with the coordination of dihydrogen, which
is required for the generation of the active species of
hydrogenation.
The scope and limitation were investigated with the
optimized conditions (Table 1, runs 11−15). A trace amount
of n-alcohol was obtained from 1-methylcyclohexene accom-
panied by iso-alcohols (19%) probably due to slow isomer-
ization of the trisubstituted cyclic alkene (run 11). A substrate
with a conjugated CC bond, β-methylstyrene, was trans-
formed to an n-alcohol as a major product (69%, run 12). An
internal alkenol and its ester, (Z)-6-nonen-1-ol and (Z)-6-
nonenyl acetate (runs 13 and 14), were converted to n-alcohol
with moderate yields (62 and 65%) and n/i ratios (9.3 and 4.6).
Finally, methyl oleate, which is a potential renewable chemical
feedstock,11 was tested as a substrate. The n-alcohol was given
as a major product (37%, n/i = 1.9) but the direct
hydrogenation of the CC bond took place as a major
problematic side reaction. A similar tendency was previously
reported in the Rh-catalyzed isomerization/hydroformylation
of methyl oleate.5j
Figure 1. Catalyst components used in this work.
isomerization/hydroformylation (Scheme 1, reaction A + B) in
comparison to Rh/phosphine or Rh/monophosphite sys-
tems.4,5
In runs 1−5 of Table 1, the sum of all the products did not
match the alkene conversion, due to the volatility of the starting
material, (Z)-2-decene. This was not problematic when (Z)-2-
tridecene was employed, as demonstrated in run 6 (>99% mass
recovery, 83% n-alcohol yield, n/i = 12).
Isomerization/Hydroformylation/Hydrogenation of
Other Internal Alkenes Catalyzed by Rh/A4N3/Shvo’s
Catalyst System. The reaction was further applied to octene
isomers (Table 1, runs 7−10). In order to compare the
difference in reactivity, the reaction was stopped at 18 h. As for
n/i selectivity, 1-octene was converted into the corresponding
alcohols and aldehydes with the highest value (n/i = 40),
followed by (Z)-2-octene (n/i = 27), (E)-2-octene (n/i = 17),
and (E)-4-octene (n/i = 16). Assuming that the (Z)-2-octene
coordinates to the metal catalyst more easily than (E)-2-octene
to undergo isomerization, the trend may be interpreted that the
substrate whose isomerization to the terminal alkene is more
facile tends to give the higher n/i selectivity. In contrast, the
yield of the obtained n-alcohol resulted in a completely
opposite trend. The highest n-alcohol yields were recorded for
(E)-2-octene and (E)-4-octene (45 and 46%), followed by (Z)-
2-octene (34%) and 1-octene (24%). Those yields reflect the
Consideration of the Selectivity-Determining Step
and Addition of Isomerization Catalyst. A selectivity-
determining step was speculated by the following control
experiment. When the three-step isomerization/hydroformyla-
tion/hydrogenation of (Z)-2-tridecene was stopped before
complete conversion, 1-tridecene was not observed by 1H
NMR spectroscopy (see the Supporting Information), which
indicated that the rate of hydroformylation of 1-tridecene
(reaction B, Scheme 1) is much faster than the in situ
formation of 1-tridecene by isomerization (reaction A, Scheme
1). Since hydroformylation of internal alkenes affords iso-
aldehydes, the products’ n/i ratios are dependent on the relative
rate of isomerization (A) over the direct hydroformylation of
internal alkenes.
On the basis of this assumption, several catalysts known to
catalyze alkene isomerization were tested as an extra additive to
improve the n/i ratio using (Z)-2-decene as a model
a
Scheme 2. Control Experiments To Elucidate the Role of Each Catalyst Component
a
Conditions: Substrate 2.0 mmol, 1,4-dioxane 4.0 mL, H2 0.25 MPa, CO 0.25 MPa, 120 °C, 18 h. a) Rh(acac)(CO)2 1.0 mol %, A4N3 2.0 mol %.
b), c) Shvo’s catalyst 1.5 mol % (Ru). d) Rh(acac)(CO)2 1.0 mol %, Shvo’s catalyst 1.5 mol % (Ru).
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Table 2. Hydrogenation of n-Undecanal by Various Combinations of Catalyst Components
run Rh(acac)(CO)2 (mol %) A4N3 (mol %) Shvo’s cat. (mol % (Ru)) conversn (%) n-alcohol (%)
other deviations from run 1
1
2
3
4
5
6
7
8
9
0
0
2.0
2.0
2.0
0
13
98
96
13
22
98
34
35
91
8.8
91
85
7.5
7.9
85
22
8.2
79
1.5
1.5
1.5
0
0
2.0
0
2.0
0
2.0
2.0
0
0
[Rh(coe)2Cl]2 1.0 mol %
1.5
1.5
0
0
tetraphenylcyclopentadienone 1.0 mol %
Ru3(CO)12 2.0 mol % (Ru)
DMA used as a solvent
0
0
0
2.0
a
Conditions: undecanal 2.0 mmol, H2 0.25 MPa, CO 0.25 MPa, 1,4-dioxane 4.0 mL, 120 °C, 18 h. Yields were determined by gas chromatography
using dodecane as an internal standard.
Scheme 3. Proposed Reaction Mechanism of Hydrogenation of Aldehyde by Shvo’s Catalyst under H2/CO Pressure2j and Trap
of Coordinative Unsaturated Species 2 by Another Ligand L
substrate.12 As a result, Ru3(CO)12 was found to improve the
n/i ratio, while maintaining the yield of n-alcohol (n/i = 23 in
run 16 compared to 18 in run 5 of Table 1). Improvement in
the n/i ratio was more prominent when methyl oleate was
employed as a substrate (n/i = 4.4 in run 17 compared to 1.9 in
run 15 of Table 1), which is the highest n/i even for the
previous reports on the two-step isomerization/hydroformyla-
tion reaction of fatty acids.5j As a result, the yield of n-alcohol
went up to 53%.
Studies on the Cooperative Interaction between the
Rh and Ru Catalysts. In order to elucidate the roles played by
each catalyst component, the control experiments shown in
Scheme 2 were carried out. Some synergetic effects of the
multiple catalysts were suggested in addition to the major role
of each catalyst, namely isomerization/hydroformylation by
Rh/A4N3 and hydrogenation by Shvo’s catalyst. The use of
Rh/A4N3 in the absence of Shvo’s catalyst resulted in
isomerization/hydroformylation of (Z)-2-decene to undecanal
with a much lower n/i value in comparison to that for the one-
pot reaction (n/i = 1.3 in Scheme 2a in comparison to n/i = 18
in run 5 of Table 1). This may be explained by the fact that
Shvo’s catalyst contributed to alkene isomerization to some
extent (Scheme 2b). The hydrogenation of undecanal by Shvo’s
catalyst was also examined under H2/CO in the absence of Rh/
A4N3 (Scheme 2c). Notably, the rate of aldehyde conversion
was much lower (13% in 18 h). On the other hand, complete
conversion of aldehyde was observed in the presence of a
catalytic amount of Rh(acac)(CO)2 (Scheme 2d). This result
indicates the cooperativity of Shvo’s catalyst and Rh(acac)-
(CO)2 in the hydrogenation under H2/CO.
By the control experiments, the coexistence of Shvo’s catalyst
and Rh(I) was confirmed to be essential and sufficient.
Hydrogenation of undecanal was performed under various
conditions (Table 2). The results shown in runs 1 and 2 are
those of Scheme 2c,d, respectively. By the mixture of
Rh(acac)(CO)2, A4N3, and Shvo’s catalyst, which is similar
to the real catalytic reaction, high conversion was observed (run
3). On the other hand, with only Rh(acac)(CO)2 or a
combination of Shvo’s catalyst and A4N3, the reaction resulted
in low conversions (run 4 and 5). These results indicate that
the coexistence of Rh(acac)(CO)2 and Shvo’s catalyst is
essential for high conversion. Acetylacetone, which is released
by the hydrogenolysis of Rh(acac) to Rh−H, is innocent
because Shvo’s catalyst with [Rh(coe)2Cl]2 was also effective
(run 6). In other possibilities, the enhanced activity might have
been derived from a cooperative effect of Rh with free
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tetraphenylcyclopentadienone or Ru carbonyl complex
(Rux(CO)y), which could be generated by the dissociation of
tetraphenylcyclopentadienone from the Ru center of Shvo’s
catalyst and the coordination of CO to the resulting Ru.
However, neither Rh(acac)(CO)2 with tetraphenylcyclopenta-
dienone nor Rh(acac)(CO)2 with Ru3(CO)12 exhibited high
activity (runs 7 and 8). These facts in runs 6−8 could be
interpreted by the notion that ligands on the Rh precursor do
not make a significant difference but coordination of
tetraphenylcyclopentadienone to Ru is essential. The cooper-
ativity between the Rh and Ru catalysts found in this three-step
reaction is in contrast to our previous studies on the two-step
reaction, hydroformylation/hydrogenation.2j In our previous
report, when the hydrogenation of undecanal was carried out
under 2.0 MPa of H2/CO in DMA as solvent at 120 °C, Shvo’s
catalyst and a Rh(acac)(CO)2/XANTPHOS/Shvo’s catalyst
mixture exhibited quite similar activity. The difference was
ascribed to the difference in solvent effects, because rapid
hydrogenation took place in DMA without assistance by Rh
(run 9).
quantitatively from 1. The amount of 1 was estimated by
assuming the rest of the Ru existed as 1.14 The rate equation
was estimated as
d[1]/dt = k1[1][XANTPHOS]
k1 = 0.48 0.01 L mol−1 min−1
When the exchange of CO of 1 and XANTPHOS was
monitored in the presence of Rh, acceleration of the process
was observed. A solution of Rh(acac)(CO)2/XANTPHOS/1
(1:2:1.5 molar ratio) in 1,4-dioxane was treated under 0.1 MPa
of H2/CO at 100 °C. As a result, 5, XANTPHOS,
2j
Rh(CO)2H(xantphos),8 and [Rh(CO)2(xantphos)]2 were
observed by 31P NMR (Scheme 5). The amounts of
Scheme 5. Reaction of 1 and XANTPHOS under H2/CO in
the Presence of Rh
In our previous report, the reaction mechanism of the
hydrogenation of undecanal by Shvo’s catalyst was proposed as
described in Scheme 3. Since 1 was quantitatively obtained by
treatment of a solution of Shvo’s catalyst under H2/CO
pressure, 1 is suggested to be the resting state. Successive loss
of CO to form 2 and coordination of dihydrogen gives the σ-
dihydrogen complex 3.13 Metal−ligand cooperative activation
of dihydrogen affords the active species 4,7 and the transfer of
the two hydrogen atoms to aldehyde7e accompanied by the
coordination of CO generates the alcohol and 1. Assuming the
mechanism is the same under the conditions of this work (0.5
MPa of H2/CO in 1,4-dioxane at 120 °C), the cooperative
effect of Rh(I) species would be the acceleration of one of
those steps.
Rh(CO)2H(xantphos), and [Rh(CO)2(xantphos)]2 were con-
stant during the reaction. Therefore, the time-dependent
variations observed by 31P NMR spectra reflected only the
reaction of 1 and XANTPHOS. In this case, the rate equation
was also estimated to be
By the NMR experiment, Rh was confirmed to accelerate the
dissociation of CO from 1 to form 2, as follows. In order to
estimate the rate of generation of 2 from 1, trapping of 2 with
another ligand to give 1-L was examined in the absence and
presence of Rh. Initially, the experiment was tried with A4N3
ligand, but it did not afford a thermodynamically stable Ru
complex, probably due to its low basicity and large substituents
on the phosphorus atoms. Alternatively, the experiment was
carried out by using XANTPHOS as a trapping agent. The
reaction of 1 with XANTPHOS (1.5:2 molar ratio) in 1,4-
dioxane under 0.1 MPa of H2/CO at 100 °C was monitored by
31P NMR spectroscopy (Scheme 4). During the reaction, only
d[1]/dt = k2[1][XANTPHOS]
k2 = 2.5 0.4 L mol−1 min−1
When the rate constants of the exchange of CO of 1 with
XANTPHOS were compared in the absence and presence of
Rh (k1 = 0.48 0.01 L mol−1 min−1 and k2 = 2.5 0.4 L mol−1
min−1), the reaction was evidently accelerated by a factor of 5
(2.5/0.48) in the presence of Rh. This result suggested that Rh
facilitates the dissociation of CO from 1 to 2, resulting in a
higher rate of the generation of active species 4 for the
hydrogenation of aldehyde.15
XANTPHOS and κ1-xantphos complex 5 were observed by 31
P
NMR, and the reaction irreversibly proceeded to form 5
Scheme 4. Reaction of 1 and XANTPHOS under H2/CO
CONCLUSION
■
In this work, we developed a Rh/bisphosphite/Shvo’s catalyst
system for the one-pot isomerization/hydroformylation/hydro-
genation of internal alkenes to corresponding homologated n-
alcohols with high n/i selectivity. Addition of an extra catalyst
for isomerization, Ru3(CO)12, enhanced the n/i ratio, especially
in the reaction of methyl oleate. The roles of each catalytic
component were clarified by the control experiments, one of
which suggested the cooperativity of Rh and Ru in the
hydrogenation of aldehyde under H2/CO. By a kinetic study of
the exchange of the CO of 1 with XANTPHOS, it was
suggested that the dissociation of CO from 1 was facilitated in
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alcohols. Details of optimization of the reaction conditions are
summarized in Table S1 in the Supporting Information.
the presence of Rh, and that accelerated the generation of active
species for hydrogenation. Although the system of this work is
still less effective compared to the currently used cobalt/
alkylphosphine system in practical aspects such as catalytic
activity, separation, cost, etc., present work would contribute to
the future developments of multiple cooperative catalyst
systems.
Tandem Isomerization/Hydroformylation/Hydrogenation of
Octene Isomers, 1-Methylcyclohexene, 2-Methylstyrene, (Z)-6-
Nonen-1-ol, and (Z)-6-Nonenyl Acetate by a Dual-Catalyst
System. The experiments were similarly performed except using
1
tridecane in place of dodecane. Products were assigned by H NMR
and/or accordance of retention time with authentic sample by GC.
Yields were determined as follows.
Octene Isomers. Yields of n-alcohol, n-aldehyde, and octane were
determined by GC with a calibration curve made with an authentic
sample. Yields of i-alcohols and unknown side products were estimated
by a calibration curve made for n-alcohol. Yields of i-aldehydes were
estimated by a calibration curve made for n-aldehyde.
EXPERIMENTAL SECTION
■
General Considerations. All manipulations involving the air- and
moisture-sensitive compounds were carried out by using standard
Schlenk techniques or a glovebox under argon purified by passing
through a hot column packed with BASF catalyst R3-11. Commercially
available anhydrous 1,4-dioxane and DMA were distilled and degassed
by freeze−pump−thaw before use. Commercially available anhydrous
toluene, hexane, and THF were passed through solvent purification
columns prior to use. Product yields were determined by a Shimadzu
GC-2014 instrument equipped with an InertCap 5MS/Sil capillary
column (0.25 i.d., 0.25 μm df, 30 m) using dodecane as an internal
standard for (Z)-2-decene and tridecane for all other substrates. NMR
spectra were recorded with JEOL JIN-ECP500 and JEOL-ECS400
spectrometers. Chemical shifts are reported in ppm relative to the
(Z)-2-Tridecene. The yield of n-alcohol was determined by 1H
NMR (δ 3.60 (t, J = 7)) using 1,1,2,2-tetrachloroethane as an internal
standard after evaporation of the solvent. Yields of i-alcohols,
tridecane, and unknown side products were estimated by GC on
comparison of integrations of the peaks with that of n-alcohol. The n/i
ratio determined by GC was consistent with the value estimated by 1H
NMR spectroscopy.
1-Methylcyclohexene. Yields of n-alcohol, n-aldehyde, and i-
aldehydes were trace amounts. Yields of i-alcohols and unknown
side products were estimated by GC with a calibration curve made for
n-alcohol.
1
residual protiated solvent for H nuclei and an external standard for
13C ((CH3)4Si) and 31P (H3PO4) nuclei. Data are presented in the
2-Methylstyrene. The E/Z ratio of the commercially available
following order: chemical shift, multiplicity (s = singlet, d = doublet, t
= triplet, m = multiplet, br = broad), coupling constant in hertz (Hz),
and signal area integration in natural numbers. NMR yields were
determined by 1H experiments with a 15 s relaxation delay using 1,3,5-
trimethoxybenzene or 1,1,2,2-tetrachloroethane as an internal stand-
ard. H2/CO mixed gas (H2:CO = 49.1:50.9) was purchased from
Suzuki-Shoukan and used without further purification. 1-Decene, (Z)-
2-decene, 1-octene, (Z)-2-octene, (E)-2-octene, (E)-4-octene, dodec-
ane, tridecane, n-undecanal, 1-methylcyclohexene, (Z)-2-methylstyr-
ene, (Z)-6-nonen-1-ol, (Z)-6-nonenyl acetate, PPh3, P(OPh)3, and
2,3,4,5-tetraphenylcyclopentadienone were purchased from TCI.
Methyl oleate and Rh(acac)(CO)2 were purchased from Aldrich.
XANTPHOS,8 BISBI,9 Shvo’s catalyst,7e Ru3(CO)12,16 [Rh-
(coe)2Cl]2,17 (Z)-2-tridecene,18 and 12j were prepared by literature
procedures. A4N3 was prepared by Mitsubishi Chemicals by a
patented procedure.10 Liquid compounds were degassed by three
freeze−pump−thaw cycles before use.
Standard Procedure of Tandem Isomerization/Hydroformy-
lation/Hydrogenation of (Z)-2-Decene by a Dual-Catalyst
System. In a 50 mL stainless steel autoclave, Rh(acac)(CO)2 (5.2
mg, 20 μmol), phosphorus ligand (40.0 μmol), and the appropriate
solvent (1.0 mL) were charged under an argon atmosphere. The
autoclave was flushed with H2/CO and stirred at room temperature
for 5 min. A solution of Shvo’s catalyst (16.3 mg, 30.0 μmol (based on
Ru atom)) in an appropriate solvent (3.0 mL) was prepared in a
Schlenk tube, and then the solution was transferred to the autoclave. A
mixture of the substrate (Z)-2-decene and dodecane ([1-decene]/
[dodecane] = 2.00) was added via syringe (550 μL, ca. 450 mg, ca. 2.0
mmol) into the autoclave. The exact amount of substrate was
determined by the change in weight of the syringe before and after
addition. The autoclave was pressurized with the appropriate pressure
of H2/CO, and the mixture was stirred at the desired temperature and
reaction time. The gas was released after the autoclave was cooled to
room temperature, and the crude product was diluted with toluene
and analyzed by gas chromatography. Peaks for n-aldehyde and n-
alcohol were assigned by comparison with authentic samples. Peaks
having retention times close to but shorter than that of n-aldehyde
were assigned as i-aldehydes. Peaks having retention time close but
shorter than n-alcohol and longer than n-aldehyde were assigned as i-
alcohols. Yields of n-undecanal, n-undecanol, and decane and recovery
of alkenes were determined by calibration curves using dodecane as an
internal standard. Yields of i-aldehydes and i-alcohols were determined
by using calibration curves made for n-aldehyde and n-alcohol,
respectively. Conversions were defined as consumption of CC
bonds because all decene isomers could potentially be converted to n-
1
starting material was determined by GC and H NMR. The crude
1
mixture was analyzed by H NMR and GC to confirm the complete
absence of CC bonds and aldehydes. The yield of n-alcohol was
determined by GC with a calibration curve made with an authentic
sample. Yields of i-alcohols, n-propylbenzene, and unknown side
products were estimated by a calibration curve made for n-alcohol. The
determined n/i ratio by GC was consistent with the value estimated by
1H NMR spectroscopy.
1
(Z)-6-Nonen-1-ol. The crude mixture was analyzed by H NMR
and GC to confirm the absence of CC bonds and aldehydes. The n-
alcohol was isolated by silica gel column chromatography
(hexane:EtOAc = 1:1 → 1:2). Yields of i-alcohols, nonanol, and
unknown side products were estimated by GC by comparing
integrations of the peaks with that of n-alcohol. The n/i ratio
1
determined by GC was consistent with the value estimated by H
NMR spectroscopy.
(Z)-6-Nonenyl Acetate. The crude mixture was analyzed by 1H
NMR and GC to confirm the absence of CC bonds and aldehydes.
1
The yield of n-alcohol was determined by H NMR (δ 3.64 (t, J = 7
Hz)) using 1,1,2,2-tetrachloroethane as an internal standard after
evaporation of the solvent. Yields of i-alcohols, nonanyl acetate, and
unknown side products were estimated by GC by comparing
integrations of the peaks with that of n-alcohol. The n/i ratio
1
determined by GC was consistent with the value estimated by H
NMR spectroscopy.
Tandem Isomerization/Hydroformylation/Hydrogenation of
Methyl Oleate by a Dual-Catalyst System. The experiment was
performed similarly for other substrates. After the gas was released,
1,4-dioxane was removed by evaporation and the resulting solid was
analyzed by 1H NMR with 1,3,5-trimethoxybenzene as an internal
standard. The recovery of CC bonds (δ 5.26−5.61 (m)) and the
yields of i-alcohols (δ 3.46−3.56 (m)), n-aldehyde (δ 9.76 (t, J = 2)),
and i-aldehydes (δ 9.55 (m), and δ 9.53 (d, J = 3)) were determined.
After the crude mixture was concentrated, silica gel column
chromatography (hexane: Et2O = 3:2 → 2:3) afforded three fractions
(Rf values are those with hexane:Et2O = 2:3 as an eluent): (1) Rf = 0.3,
pure n-alcohol; (2) Rf = 0.9, mixture of isomers of starting material
with different positions of CC bonds and directly hydrogenated
product; (3) Rf = 0.35, mixture of i-alcohols and unknown side
products. The yield of directly hydrogenated product was determined
by a 1H NMR spectrum of the mixture (2). The colorless solid
obtained by recrystallization from hot AcOEt solution of fraction (1)
was submitted for elemental analysis.
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Journal of the American Chemical Society
Article
1
Methyl 19-Hydroxynonadecanoate. To the sample for the H
NMR experiment was added 1 drop of D2O to eliminate the signal of
H2O in CDCl3 (s, 1.56 ppm): 1H NMR (CDCl3, 500 MHz) δ 3.66 (s,
3H), 3.63 (t, J = 8.1, 2H), 2.30 (t, J = 7.4, 2H), 1.65−1.51 (m, 4H),
1.38−1.20 (m, 28H); 13C NMR (CDCl3, 101 MHz) δ 174.5 (4°), 63.2
(CH2), 51.6 (CH3), 34.3 (CH2), 33.0 (CH2), 29.8 (CH2), 29.7 (CH2)
29.6 (CH2), 29.4 (CH2), 29.3 (CH2), 25.9 (CH2), 25.1 (CH2); mp 67
°C; IR (neat, cm−1) 3279 (O−H), 2916 (C−H), 2847 (C−H), 1740
(CO). Anal. Calcd for C20H40O3: C, 73.12; H, 12.27. Found: C,
72.86; H, 12.43. 1H and 13C NMR spectra are given in the Supporting
Information (Figures S1 and S2).
0.1 MPa of H2/CO and heated in an oil bath at 100 °C. After each
period of heating, the solution was analyzed by 31P NMR spectroscopy
(256 scans). The singlet at −17 ppm was assigned to XANTPHOS,8
and resonances at 39 and −22 ppm were assigned to two
nonequivalent phosphorus atoms of dicarbonyl(tetraphenylcyclo-
pentadienone)(xantphos-κ1P)ruthenium (5).2i The amounts of
phosphorus-containing compounds were estimated by the ratio of
the integrations of the signals by assuming that the sum of the
integrations of all signals corresponded to 12.0 μmol of phosphorus
atom. The amount of 1 was estimated by assuming all of the Ru
species except 5 was 1. The time courses of each compound, the plot
to determine k1, and the NMR spectra are shown in the Supporting
Information (Figures S4 and S6). The experiment was carried out
twice, and k1 was reported as the mean value and deviation of these
two experiments.
Tandem Isomerization/Hydroformylation/Hydrogenation of
Methyl Oleate by a Ternary Catalyst System. In a 50 mL stainless
steel autoclave, Rh(acac)(CO)2 (5.2 mg, 20 μmol), A4N3 (42.9 mg,
40.0 μmol), and 1,4-dioxane (1.0 mL) were charged under an argon
atmosphere. The autoclave was flushed with H2/CO (1/1 molar ratio)
gas, and the mixture was stirred at room temperature for 5 min. A
solution of Shvo’s catalyst (16.3 mg 30.0 μmol (based on Ru)) and
Ru3(CO)12 (5.3 mg, 20 μmol (based on Ru)) in 1,4-dioxane (3.0 mL)
was prepared in a Schlenk tube, and then the solution was transferred
to the autoclave. Methyl oleate (680 μL, ca. 2.0 mmol) was added via
syringe into the autoclave. The exact amount of substrate was
determined by the change in weight of the syringe before and after
addition. The autoclave was pressurized with 0.5 MPa of H2/CO and
the mixture stirred at 120 °C for 36 h. The gas was released after the
autoclave was cooled to room temperature. Yields were determined as
described above.
Isomerization/Hydroformylation of (Z)-2-Decene by Rh-
(acac)(CO)2/A4N3. In a 50 mL stainless steel autoclave, Rh(acac)-
(CO)2 (5.2 mg, 20 μmol), A4N3 (42.9 mg, 40.0 μmol), and 1,4-
dioxane (4.0 mL) were charged under an argon atmosphere. The
autoclave was flushed with H2/CO gas, and a mixture of (Z)-2-decene
and dodecane ([(Z)-2-decene]/[dodecane] = 2.00) was added via
syringe (550 μL, ca. 450 mg, (Z)-2-decene 2 mmol) into the autoclave.
The exact amount of substrate was determined by the change in
weight of the syringe before and after addition. The autoclave was
pressurized with 0.5 MPa of H2/CO, and the mixture was stirred at
120 °C for 18 h. The gas was released after the autoclave was cooled to
room temperature. Yields were determined similarly as explained
above.
Isomerization of (Z)-2-Decene by Shvo’s Catalyst. In a 50 mL
stainless steel autoclave, were placed Shvo’s catalyst (16.3 mg, 30.0
μmol), 1,4-dioxane (4.0 mL), and (Z)-2-decene. The autoclave was
pressurized by 0.5 MPa of H2/CO, and the mixture was stirred at 120
°C for 18 h. The gas was released after the autoclave was cooled to
room temperature. Yields were determined similarly as explained
above.
Hydrogenation of n-Undecanal by Various Combinations of
Catalyst Components. In a 50 mL stainless steel autoclave were
placed the appropriate catalyst, solvent (4.0 mL), and a mixture of n-
undecanal and dodecane as an internal standard ([undecanal]/
[dodecane] = 2.00) (640 μL, ca. 510 mg, undecanal 2 mmol). The
autoclave was pressurized by 0.5 MPa of H2/CO, and the mixture was
stirred at 120 °C for 18 h. The gas was released after the autoclave was
cooled to room temperature. Yields were determined similarly as
explained above.
Estimation of the Rate of Exchange of CO of 1 with
XANTPHOS in the Presence of Rh. In a J. Young valve NMR tube
were added solutions of Rh(acac)(CO)2 (0.150 M in 1,4-dioxane, 200
μL, corresponds to 3.0 μmoL of Rh(acac)(CO)2) and XANTPHOS
(0.0300 M in 1,4-dioxane, 200 μL, corresponds to 6.0 μmoL of
XANTPHOS) under Ar, and the mixture was allowed to stand for 5
min. Then a solution of 1 (0.0225 M in 1,4-dioxane 200 μL,
corresponds to 4.5 μmoL) was added. The solution was degassed by
three freeze−pump−thaw cycles to fill it with 0.1 MPa of H2/CO and
heated in an oil bath at 100 °C. After each period of heating, the
solution was analyzed by 31P NMR spectroscopy (256 scans). The
singlet at −17 ppm was assigned to XANTPHOS,8 and the singlets at
39 and −22 ppm were assigned to two nonequivalent phosphorus
atoms of dicarbonyl(tetraphenylcyclopentadienone)(xantphos-κ1P)
ruthenium (5).2i The doublet at 21 ppm (J = 122) was assigned to
dicarbonylhydrido(xantphos)rhodium,8 and the doublets at 8 (J =
134) and 1 ppm (J = 134) were assigned to dicarbonyl(xantphos)-
rhodium dimer.2j The amounts of phosphorus-containing compounds
were estimated by the ratio of the integrations of the signals by
assuming that the sum of the integrations of all the signals
corresponded to 12.0 μmol of phosphorus atom. The amount of 1
was estimated by assuming that all of the Ru species except 5 was 1.
The time courses of each compound, the plot to determine k2, and the
NMR spectra are shown in the Supporting Information (Figures S5
and S7). The experiment was carried out twice, and k2 was reported as
the mean value and deviation of these two experiments.
ASSOCIATED CONTENT
* Supporting Information
■
S
Tables and figures giving the entire optimization of catalysts
and conditions, screening of isomerization catalysts, NMR
spectra, and plots determining rate constants k1 and k2. This
material is available free of charge via the Internet at http://
pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
E-mail for K.N.: nozaki@chembio.t.u-tokyo.ac.jp.
■
Notes
The authors declare no competing financial interest.
Evidence for the Absence of Terminal Alkene during
Isomerization/Hydroformylation/Hydrogenation of (Z)-2-Tri-
decene. The experimental procedure was same as that explained
above, except that the reaction was stopped after 6 h. There was no
evidence of 1-tridecene (δ 5.86−5.77 (m, 1H), 5.02−4.91 (m, 2H)).
The selected region of the obtained NMR spectrum is shown in Figure
S3 in the Supporting Information.
Estimation of the Rate of Exchange of CO of 1 with
XANTPHOS in the Absence of Rh. In a J. Young valve NMR tube
were added solutions of XANTPHOS (0.0300 M in 1,4-dioxane, 200
μL, corresponds to 6.0 μmoL of XANTPHOS), tricarbonyl(2,3,4,5-
tetraphenylcyclopentadienone)ruthenium (1; 0.0225 M in 1,4-dioxane
200 μL, corresponds to 4.5 μmoL), and 1,4-dioxane (200 μL). The
solution was degassed by three freeze−pump−thaw cycles to fill it with
ACKNOWLEDGMENTS
■
This work was supported by the Funding Program for Next
Generation World-Leading Researchers, Green Innovation.
K.T. is grateful to the Japan Society for the Promotion of
Science (JSPS) for a Research Fellowship for Young Scientists.
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