Rhodium-catalyzed nonisomerizing hydroformylation of methyl oleate applying lactame-based phosphoramidite ligands

Article abstract of DOI:10.1021/cs500274n

The rhodium-catalyzed hydroformylation of methyl oleate (MO) with new monodentate phosphoramidite ligands 1a-d is investigated here. The ligands are characterized by lactam rings of different size (four-to seven-membered rings). In mild conditions (synthesis gas pressure: 30 bar, 80°C), the rhodium catalysts based on the P-azetidinone phosphoramidite 1a gave within 6 h complete conversion and produced mainly methyl 9-and 10-formylstearate (MFS) with 99% chemoselectivity. In the hydrolysis test, phosphoramidite 1a was also the most stable. This was additionally confirmed by density functional theory calculations.

Full text of DOI:10.1021/cs500274n

Research Article
pubs.acs.org/acscatalysis
Rhodium-Catalyzed Nonisomerizing Hydroformylation of Methyl
Oleate Applying Lactame-Based Phosphoramidite Ligands
§
,§
§
§
§
§
̈
Eduard Benetskiy, Susan Luhr,* Marcelo Vilches-Herrera, Detlef Selent, Haijun Jiao, Lutz Domke,
†
†,∥
,§,‡
̈
Katrin Dyballa, Robert Franke, and Armin Borner*
§
†
∥
‡
Leibniz-Institut fu
Evonik Industries AG, Paul-Baumann-Str. 1, D-45772 Marl, Germany
Lehrstuhl fur Theoretische Chemie, 44780 Bochum, Germany
Institut fur Chemie der Universitat Rostock, A.-Einstein-Str. 3a, 18059 Rostock, Germany
S Supporting Information
̈
̈
r Katalyse an der Universitat Rostock e.V., A.-Einstein-Str. 29a, 18059 Rostock, Germany
̈
̈
̈
*
ABSTRACT: The rhodium-catalyzed hydroformylation of
methyl oleate (MO) with new monodentate phosphoramidite
ligands 1a−d is investigated here. The ligands are characterized
by lactam rings of different size (four- to seven-membered
rings). In mild conditions (synthesis gas pressure: 30 bar, 80 °C),
the rhodium catalysts based on the P-azetidinone phosphor-
amidite 1a gave within 6 h complete conversion and produced
mainly methyl 9- and 10-formylstearate (MFS) with 99%
chemoselectivity. In the hydrolysis test, phosphoramidite 1a
was also the most stable. This was additionally confirmed by
density functional theory calculations.
KEYWORDS: hydroformylation, methyl oleate, nonisomerizing, phosphoramidite, rhodium
INTRODUCTION
several impurities are usually present in a biotechnically
generated feed stock like water, fatty alcohols, wax esters,
hydrocarbons, tocopherols, phenols, pigments, phospholipids,
and triterpenic acids. During storage, the composition can
be changed due to oxidation. These compounds can poison or
decompose sensitive hydroformylation catalysts, in particular
when the latter are used only in small concentrations.
■
The homogeneously catalyzed hydroformylation of olefins is
one of the most important industrially applied transformations
of olefins into aldehydes. Up to now, required starting material
is derived from petrochemical sources. However, unsaturated
fatty acid derivatives derived from vegetables oils as soybean,
linseed, safflower, and olive oil have also attracted increasing
10
1
2
Pioneering work in the hydroformylation of fatty acids was
attention with respect to sustainable chemistry. The aldehydes
11,12
completed about 50 years ago by Lai, Naudet, and Ucciani.
These first investigations were carried out with methyl oleate
MO) as substrate using an unmodified cobalt catalyst [Co (CO) ]
that are formed can be used as intermediates in several
3
applications. Most common is the subsequent reduction of the
(
2
8
formyl and/or ester group, which gives rise to primary alcohols.
The latter are particularly valuable as components in biobased
at high synthesis gas pressure (240−310 bar) and a temperature of
175−190 °C. Under these conditions, formed aldehydes were
immediately reduced to the corresponding alcohols. More detailed
investigations by Pryde showed that at least eight isomeric alcohols
4
plasticizers for polyvinyl chloride (PVC), in novel polyur-
5
6
ethane elastomers, or in hyperbranched polyols. Another
7
application is the use as biodegradable lubricants.
13
were formed. In contrast, the groups of Frankel and Friedrich
obtained exclusively aldehydes under milder conditions (<70 bar,
Due to the presence of sometimes multiple double bonds in
different geometries and positions as well as the presence of
functional groups (mainly carboxylic groups), know-how
accumulated in the hydroformylation of unfunctionalized
olefins cannot be simply applied to the conversion of fatty
1
00−120 °C) and by using a PPh -modified rhodium catalysts
3
14
supported on heterogeneous surfaces (CaCO , Al O , or C).
3
2
3
Mainly C - and C -formylstearates were formed in an almost
9
10
3
quantitative yield. Under these conditions, hydrogenation of the
acid compounds. Migration of double bonds, isomerization of
Z/E-isomers, and hydrogenation of olefins and products may
affect or even block the hydroformylation. Another side reaction
8
Received: March 4, 2014
Revised: May 13, 2014
Published: May 19, 2014
which may complicate the hydroformylation of fatty acids is de-
9
carbonylation catalyzed by modified Rh complexes. Moreover,
©
2014 American Chemical Society
2130
dx.doi.org/10.1021/cs500274n | ACS Catal. 2014, 4, 2130−2136

ACS Catalysis
Research Article
yielded aldehyde was not observed even when syngas was replaced
different reaction conditions. Therefore, it is not possible to
make a meaningful comparison between ligand structure and
reactivity or chemo/regioselectivity. In addition the stability of
modifying ligands was not addressed at all, although several
studies emphasize the importance of this issue with respect to
by pure hydrogen. Also, a rhodium catalyst modified with
15
P(OPh) was quite efficient under similar conditions.
3
Later, van Leeuwen and co-workers applied a homogeneous
rhodium catalyst based on the sterically hindered ligand tris-
23
(
2-tert-butyl-4-methylphenyl)phosphite in the same transforma-
industrial hydroformylation processes.
16
tion under 20 bar syngas pressure and 100 °C (Rh/L = 1/25).
Therefore, we initiated a study on the synthesis of a new
class of phosphorus ligands covering a set of strongly related
individuals with the aim to test them in the hydroformylation
of MO. As a basic structure, monophosphoramidites 1 bearing
lactam units of different ring size were chosen.
A fast isomerization of MO into the trans-configurated fatty acid
ester methyl elaidate (ME) was noted prior to the hydroformylation.
Within 1.2 h, when a 50% conversion of MO and ME was achieved,
regioisomeric methyl formylstearates (MFS) were obtained with
49% yield. It was concluded that ME is hydroformylated much
slower than MO. The use of a technical-grade substrate containing
also methyl linoleate resulted in a complex mixture of products.
Da Rosa and co-workers used RhH(CO)(PPh ) as a
3
3
17
precatalyst for the hydroformylation of MO. They achieved
quantitative conversion along with a high selectivity toward
the formation of aldehydes (80−91%) when an excess of PPh
3
(
PPh /Rh = 10) was applied under 40 bar of syngas pressure
3
(
CO/H = 2:1) at 100 °C. The same authors reported that
2
Usually phosphoramidites are employed as a phosphitylation
reagent on the way to phosphite ligands. Their benefits also as
monodentate ligands for hydroformylation catalysts have been
18
RhH(CO)(PPh ) gives rise to a similar catalytic performance.
Notably, catalysts generated from RhCl ·3H O, [Rh(OMe)-
3
3
3
2
24,25
(cod)] or Rh(CO) (acac) were inferior. Recently, Monflier and
2 2
recognized for only a couple of years.
The nitrogen sub-
co-workers gave evidence that the hydroformylation of MO can
be advantageously carried out in aqueous media with Rh-TPPTS
stituent can be used for the tuning of steric and electronic
properties. Especially electron-withdrawing amide groups should be
advantageous, because ligands with strong π-accepting properties
[trisodium salt of 3,3′,3″-phosphinidynetris(benzenesulfonic acid]
19
26
as catalyst and activated carbon as an additive. The reaction
proceeded under 50 bar of syngas pressure at 80 °C and resulted
in a high conversion (93−95%) and regioselectivity (97%) for both
pure and technical grade MO. The group of Suarez investigated
RhH(CO)(PPh ) as a catalyst in an ionic liquid for the biphasic
enhance the activity of rhodium-based hydroformylation catalysts.
Interestingly, such structures have never been tested in this
reaction, probably due to the assumed high hydrolysis
27−29
sensitivity.
A few examples concern chiral binaphthol
3
3
phosphoramidites with a N-sulfonamide moiety suggested
30
hydroformylation (CO/H = 2:1, 40 bar, 100 °C) of technical-
grade biodiesel and noted consecutive reactions like hydrogenation
and decarbonylation particularly with an excess of PPh3.
Behr and co-workers observed in the hydroformylation of
MO (10 bar, 115 °C) the formation of methyl ω-formylstearate
in a yield of 26% yield using a rhodium catalyst based on the
bidentate ligand BIPHEPHOS. The formation of the linear
product can be forced by using a ternary Rh/Ru/Ru-catalyst
by Reek et al. for rhodium-catalyzed asymmetric hydrogenation.
2
N-Acyl-phosphoramidites, which are part of five-membered
heterocycles, were tested by Takeuchi et al. in the iridium
asymmetric alkylation, where an additional metal−ligand inter-
20
31
action via the carboxylic amide group was assumed.
In this study, we will report on the synthesis of these new
monodentate phosphoramidites and their evaluation as ligands
in the rhodium-catalyzed hydroformylation of MO. The
assessment of their stability toward water by hydrolysis
experiments and modeling will complete this study.
21
22
system as shown by Nozaki’s group. At a syngas pressure of
.5 bar and a temperature of 120 °C, 19-hydroxynonadecanoic
2
acid methyl ester was isolated in a yield of 53%.
RESULTS AND DISCUSSION
The above evidence indicates that in strong contrast to the
hydroformylation of petro-based olefins, up to now only a few
phosphorus ligands have been tested in the reaction with fatty
acid derivatives. Moreover, most results were obtained under
■
Synthesis of Phosphoramidites. Phosphoramidites 1
were prepared in a three-step sequence in overall yields of
47−50% starting from 2,4-di-tert-butylphenol (2, Scheme 1).
Scheme 1. Synthesis of Phosphoramidites
2
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Scheme 2. Intermediates and Products in the
Hydroformylation of Methyl Oleate
Figure 2. Variation of the temperature in the hydroformylation of
methyl oleate. Conditions: 20 bar, 0.11 mol % Rh(acac)(CO)2,
1
a/Rh = 25, 1 mmol methyl oleate, 10 mL of toluene, t = 6 h. Olefin =
MO% + ME%; for abbreviations, compare Figure 1
the yielded complex [Rh(acac)(CO)(1a)] was characterized in the
31
P NMR spectrum by a doublet at δ 131.3 (JPRh = 276 Hz ppm).
The hydroformylation was carried out with a Rh/L ratio of 1/25.
The distribution of regioisomeric aldehydes in the hydroformyla-
tion product was analyzed following an established procedure of
34
Frankel et al. Due to this procedure, formyl products were
subjected to air-oxidation in the presence of the remaining catalyst
in order to obtain the corresponding carboxylic acids. Esterification
with BF -methanol gave a mixture of methyl esters, which were
3
finally analyzed by GC/MS.
Variation of Syngas Pressure. The influence of the syngas
pressure on the hydroformylation was investigated by
increasing the pressure stepwise from 10 to 60 bar at a
Figure 1. Variation of syngas pressure in the hydroformylation of
methyl oleate. Conditions: 0.11 mol % Rh(acac)(CO) , 1a/Rh = 25,
2
1
.0 mmol methyl oleate, 10 mL of toluene, 80 °C, 6 h; MFS = methyl
constant ratio of CO/H = 1:1 at 80 °C in toluene. In all trials,
2
formylstearate, MO = methyl oleate, ME = methyl elaidate, MS =
methyl stearate.
full conversion (>99%) was noted (Figure 1/Table 1). Already
at 10 bar, high yields of isomeric aldehydes can be found. Under
the same pressure the trans-isomerization product ME was
detected to an extent of 6%. It also underwent hydroformylation
but more slowly than the cis-isomer (Run 1), which confirms
In the first step, the phenol was coupled with MnO in refluxing
2
32
heptane to give 2,2′-biphenol 3. This compound was treated
16
with 1 equivalent of phosphorus trichloride and an excess of
observations of van Leeuwen with a Rh-monophosphite catalyst.
33
triethylamine in toluene to afford phosphorchloridite 4. The
latter was finally condensed with the corresponding lactam in
the presence of triethylamine as HCl-scavenger.
Hydroformylations. Phosphoramidites 1a−d were used as
ligands in the rhodium-catalyzed hydroformylation of methyl
oleate (MO) (Scheme 2). In this reaction, besides the desired
methyl formylstearate (MFS) isomers, the isomerized olefin,
methyl elaidate (ME), as well as the hydrogenation product,
methyl stearate (MS), can be formed.
With increasing syngas pressure, the chemoselectivity toward
the hydroformylation was also improved affording finally the
35
desired aldehydes in 99% yield (entry 4 and 5). The product
was identified as a mixture of 9- and 10-MFS. Careful analysis
by GC/MS showed traces of minor isomers 8-, 11-, 12-, and
13-MFS (see Supporting Information).
Variation of Reaction Temperature. In turn, the
hydroformylation of MO was conducted at different reactions
temperatures (60 to 140 °C) using a constant syngas pressure
of 20 bar in toluene (Figure 2/Table 2). Also in these
experiments, the conversions were good or excellent (up to
>99%). The yield of MFS increased gradually from 89.9% up to
98.6%. But by enhancing the temperature to 120 and 140 °C,
The investigations were started performing a parameter
screening using 1a as ligand. For characterization, the
precatalyst was generated by reaction of Rh(acac)(CO) with
2
an equimolar amount of ligand in toluene. After stirring for 4 h,
a
Table 1. Hydroformylation of MO at Different Syngas Pressures with 1a as Ligand
b
c
c
c
c
d
entry
p [bar]
conversion [%]
MO [%]
MFS [%]
ME [%]
MS [%]
regioselectivity
1
2
3
4
5
10
20
30
40
60
99.4
99.8
99.2
99.9
99.9
b
0.6
0.2
0.8
93.2
97.7
98.4
99.0
99.0
6.1
1.9
0.2
0.2
0.2
0.2
C5−C17
C8−C13
C8−C13
C8−C13
C8−C12
a
c
d
Reaction conditions: see Figure 1. Conversions were determined by GC (100 − % GC yield of MO). Determined by GC. C , n = carbon atom
where the formyl group is linked.
n
2
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Research Article
a
Table 2. Hydroformylation of MO at Several Reaction Temperatures with 1a as Ligand
b
c
c
c
d
entry
T [°C]
conversion [%]
olefin (MO + ME)[%]
MFS [%]
MS [%]
regioselectivity
1
2
3
4
5
60
80
99.0
99.8
99.9
99.7
98.6
10.0
2.1
89.9
97.7
98.6
95.9
85.9
0.1
0.2
0.3
1.4
2.8
C9−C12
C8−C13
C3−C18
C3−C18
C3−C18
100
120
140
1.1
3.1
11.3
a
b
Reaction conditions: CO/H = 1:1, 20 bar; for other conditions, see Figure 1. Conversions were determined by GC (100 − % GC yield of MO).
Determined by GC. C , n = carbon atom where the hydroformylation took place.
2
c
d
n
a
Table 3. Hydroformylation of MO with Different Ligands
b
c
c
c
c
d
ligand
conversion [%]
MO [%]
MFS [%]
ME [%]
MS [%]
regioselectivity
1
1
1
1
a
b
c
99.8
91.5
88.7
98.7
59.0
99.6
0.2
8.5
97.7
32.9
32.2
89.1
51.8
96.0
1.9
58.1
56.2
9.3
0.2
0.5
0.3
0.3
0.1
0.2
C8−C13
C7−C14
C7−C13
C8−C13
C9−C12
C8−C13
11.3
1.3
d
PPh3
41.0
0.4
7.1
e
Alkanox 240
3.4
a
b
Reaction conditions: CO/H = 1:1, 20 bar; for other conditions, see Figure 1. See also ref 36. Conversions were determined by GC (100 − % GC
yield of MO). Determined by GC. C , n = carbon atom where the hydroformylation took place. Tris[2,4-di(tert-butyl)phenyl]phosphite.
2
c
d
e
n
respectively, the yield of MFS decreased to 95.9% and 85.9%,
respectively. Remarkably, an increase in the formation of olefins
and MS was noted (entries 4 and 5). Apparently, at high
temperatures, hydroformylation is accompanied by decarbon-
ylation and olefin hydrogenation. At 60 or 80 °C, isomerization
of the double bond is small; however, at higher temperatures,
this reaction is forced, and consequently, several regioisomeric
aldehydes are formed finally (entries 3−5).
Variation of Solvent. By changing the solvent to methanol,
the conversion, along with the yield of MFS, dropped
drastically to 39.1% and 25.7%, respectively. Nevertheless
with this solvent the best regioselectivity, exclusively a mixture
of C9- and C10-formyl compound, was observed. The
formation of dimethylacetals by tandem reaction of the
aldehyde formed with the solvent did not take place.
we tested it under identical reaction conditions. All new
phosphoramidite ligands 1 induced superior reactivities and
chemoselectivities. PPh formed a very sluggish catalyst (59.0%
3
conversion) and yielded only 51.8% of MFS. It should be noted
that only 7.1% ME is formed, which corresponds to a low
isomerization activity. The regioselectivity was slightly improved.
Moreover, we were pleased to see that the four-ring lactam
1a even successfully competed with tris[(di(2-tert-butyl)phenyl]-
phosphite (Alkanox 240), one of the most prominent mono-
37
phosphites used in rhodium-catalyzed hydroformylation.
Hydrolysis. In a subsequent investigation, the stability of
phosphoramidites 1a−d toward water was tested. For this
purpose, a 0.0175 M solution of phosphoramidite in 1,4-
dioxane was treated with water at 85 °C in a sealed NMR tube.
3
1
The degree of decomposition was analyzed by P NMR
Screening of Ligands. The hydroformylation experiments
under variation of the ligands were carried out at 80 °C where
best reactivity and regioselectivity were found in proceeding
experiments (Table 3). Although a syngas pressure above of 30
bar lead to superior chemo- and regioselectivity with ligand 1a,
we conducted the reactions at 20 bar in order to identify more
pronounced differences between ligands.
spectroscopy using tri(n-octyl)phosphine oxide as an internal
standard. Notably, huge differences were observed (Figure 3).
38
There is no clear trend between activity and ring size of the
lactam ligands. Thus, the best reactivity was found with the
four-membered ring lactam ligand 1a with 99.8% conversion
and 97.7% yield of MFS. In the case of the five- and six-
membered ring lactam ligands, 1b and 1c, the conversion
decreased to 91.5% and 88.7%, respectively. Only around 32%
of MFS was formed. This could be due to the high cis/trans-
isomerization tendency of catalysts of 1b and 1c, which gives
ME in 58.1% and 56.2% yield. Obviously, the lowered
hydroformylation activity with this isomeric substrate decreases
the final yield of MFS. Unexpectedly, the seven-ring lactam 1d
led to the production of 89.1% yield of MFS along with a high
conversion of 98.7%. In all trials, the formation of MS was at a
minimum (<0.5%). With regard to the regioselectivity of the
reaction with all ligands 1a−d, mainly a mixture of 9- and
Figure 3. Resistance of lactam-based phosphoramidites 1a−d toward
hydrolysis. Results for the reaction of a 0.0175 M solution in dioxane-
1,4 with 100 mol equivalents of water at 85 °C. The time (h) required
for full decomposition is given.
Poor hydrolysis resistance was observed for phosphoramidites
with large lactam rings 1c and 1d, which decomposed within a
few hours. Phosphoramidite 1b, bearing a five-membered
lactam ring, proved to be more stable. Surprisingly, azetidinone-
phosphoramidite 1a, which performed best as ligand in the
1
0-MFS was formed; only traces of other isomers were detected.
In order to compare these results with PPh , which present a
3
standard ligand in technical nonisomerizing hydroformylation,
2
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ACS Catalysis
Research Article
hydroformylation of MO, was most stable. The compound was
fully hydrolyzed only after about 20 days.
These energetic data are in line with the computed relative stability
based on the exchange reaction discussed above.
39
Computational Calculations. In order to understand the
relative stability of phosphoramidites 1a−d, we have carried out
B3LYP/TZVP DFT calculations (the computational details are
given in the Supporting Information). At first, we computed the
relative stability caused by the rings of different sizes on the
In addition, the computed activation free energies (ΔG ) for
a
the hydrolysis also reveal that the reaction of 1a with one water
molecule via the four-membered transition state (TS) has the
highest activation barrier (49.71 kcal/mol), tightly followed
by 1b (49.34 kcal/mol), whereas the barriers of 1c and 1d
are somewhat lower (48.99 and 46.36 kcal/mol, respectively).
It is also shown that the activation free energy for 1a with two
water molecules involving a six-membered transition-state
structure is approximately the same as found for the four-
membered transition-state structure with only one water
molecule. In contrast, activation free energies for 1b−1d with
the six-membered transition-state structures are very close, and
they are higher than those for the four-membered transition-state
structures. In conclusion, both kinetic and thermodynamic
parameters evidence the extremely enhanced hydrolysis stability
of 1a, which is in full agreement with the experimental results.
Indeed, such energetic performances correlate with the
electronic properties of the P−N bond as listed in Table 5. For
example, the P−N bond length increases from 1a to 1d
continually, and the same is also found for the Wiberg bond
indexes; however, the orbital occupancy decreases accordingly.
The atomic hybrid contributions from NLMO analysis on both
P and N atoms show clearly that the shorter P−N distance in
basis of the exchange reaction (Scheme 3/Table 4, ΔE ). For
x
Scheme 3. Exchange Reaction for the Calculation of the
Gibbs Free Energy
Table 4. B3LYP/TZVP Computed Exchange Energies
(
ΔE , kcal/mol), Reaction Free Energy (ΔG, kcal/mol), and
x
Activation Free Energy (ΔG , kcal/mol) of Hydrolysis
a
ΔEx
ΔG
ΔG (TS-4MR)
ΔG (TS-6MR)
a
a
1
1
1
1
a
b
c
0.00
3.36
6.26
6.09
−11.88
−12.54
−18.14
−17.97
49.71
49.34
48.99
46.36
48.96
51.06
51.53
51.50
d
1
a originates from the stronger s character of the hybrid
orbitals, whereas the longer P−N bond in 1d is due to the
stronger p character of the hybrid orbitals. The highest thermo-
dynamic stability of 1a has its electronic origin. In contrast, the
computed natural charge of both P and N atoms, which reflects
their total bonding effects, does not show a clear trend.
n = 2−4, the calculated Gibbs free energy for the exchange
reaction is endergonic by 3.36, 6.26, and 6.09 kcal/mol,
respectively. This energetic order indicates clearly that 1a is
most stable, followed by 1b, whereas 1c and 1d are the least
stable.
SUMMARY AND CONCLUSIONS
In addition, we also calculated the thermodynamic (ΔG) and
■
kinetic data (ΔG ) of the hydrolysis (Scheme 4/Table 4).
a
A set of new phosphoramidites bearing lactam rings was synthesized
and evaluated as ligands in the rhodium-catalyzed hydroformylation
of methyl oleate under mild conditions (syngas pressure: 20 bar,
Scheme 4. Reaction of Phosphoramidites with Water
8
0 °C). The size of the lactam ring has a significant influence on all
reaction parameters, like degree of E/Z-isomerization, conversion,
yield of methyl formylstearate, and regioselectivity. Superior results
were obtained with a ligand based on a four-membered lactam ring.
Remarkably, the ligand which performs best in the catalytic reaction
is also by far the most stable toward water. Preliminary experiments
40
in the hydroformylation of n-octenes showed a similar trend.
Up to now, it is not clear whether such a correlation between
hydroformylation activity and hydrolysis stability exist or whether
we witnessed only a random coincidence.
ASSOCIATED CONTENT
■
As detailed in Table 4, hydrolyses of 1a−d are exergonic in each
case. However, the computed free energies (ΔG) clearly show that
the hydrolysis of 1a is least exergonic (−11.88 kcal/mol), followed
by that of 1b (−12.54 kcal/mol). The reaction of 1c and 1d with
water is more exergonic (−18.14 and −17.97 kcal/mol). This
gives evidence that 1a is most inert toward the attack of water.
*
S
Supporting Information
Synthesis and characterization of phosphoramidites 1a−d,
hydroformylation procedures, characterization of products,
and computational details. This material is available free of
charge via the Internet at http://pubs.acs.org
Table 5. Computed P−N Distance (r, Å), Wiberg Bond Index (WBI), and Orbital Occupancy, As Well As Natural Charge (δ),
x
Percentage Contribution (%), and the Atomic Hybrid Contribution (sp ) of P and N Atoms from Natural Localized Molecular
Orbital (NLMO) Analysis
rP−N
WBI
occupancy
δP
δN
P%
N%
P(spx)
N(spx)
1
1
1
1
a
b
c
1.737
1.752
1.780
1.782
0.785
0.766
0.744
0.745
98.9%
98.5%
98.1%
98.1%
1.499
1.514
1.508
1.513
−0.747
−0.736
−0.715
−0.727
23.34
24.26
24.85
24.26
74.80
74.47
73.62
74.19
4.89
5.07
5.30
5.39
1.77
2.16
2.80
2.38
d
2
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ACS Catalysis
AUTHOR INFORMATION
Research Article
1
1
(
4. (c) Friedrich, J. P.; List, G. R.; Sohns, V. E. J. Am. Oil Chem. Soc.
973, 50, 455−458.
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16) Muilwijk, K. F.; Kamer, P. C. J.; van Leeuwen, P. W. N. M. J.
■
Corresponding Authors
*
E-mail: susan.luehr@catalysis.de.
E-mail: armin.boerner@catalysis.de.
*
(
Notes
Am. Oil Chem. Soc. 1997, 74, 223−228.
17) Mendes, A. N. F.; Gregorio, J. R.; da Rosa, R. G. J. Braz. Chem.
Soc. 2005, 16, 1124−1129.
18) Mendes, A. N. F.; da Rosa, R. G.; Gregor
012, 35, 1940−1944.
19) Boulanger, J.; Ponchel, A.; Bricout, H.; Hapiot, F.; Monflier, E.
Eur. J. Lipid Sci. Technol. 2012, 114, 1439−1446.
20) Ramalho, H. F.; di Ferreira, K. M. C.; Machado, P. M. A.;
The authors declare no competing financial interest.
(
́
ACKNOWLEDGMENTS
(
2
(
́
io, J. R. Quim. Nova
■
We acknowledge highly skilled technical assistance by Mrs.
Kerstin Romeike, Mrs. Maria Lange, and Mrs. Heike Borgwaldt.
We are grateful to the analytical department of LIKAT, mainly
Dr. Christine Fischer and Mrs. Susann Buchholz, for chromato-
graphic analyses. We thank Evonik Industries for financial
support.
(
Oliveira, R. S.; Silva, L. P.; Prauchner, M. J.; Suarez, P. A. Z. Ind. Crops
Prod. 2014, 52, 211−218.
(21) Behr, A.; Obst, D.; Westfechtel, A. Eur. J. Lipid Sci. Technol.
2
005, 107, 213−219.
(22) Yuki, Y.; Takahashi, K.; Tanaka, Y.; Nozaki, K. J. Am. Chem. Soc.
013, 135, 17393−17400.
23) Van Leeuwen, P. W. N. M.; Chadwick, J. C. Homogeneous
Catalysts, Activity − Stability − Deactivation; Wiley-VCH: Singapore,
011.
24) (a) Van Rooy, A.; Burgers, D.; Kamer, P. C. J.; van Leeuwen, P.
W. N. M. Recl. Trav. Chim. Pays-Bas 1996, 115, 492−498. (b) Breikss,
A. I.; Burke, P. M.; Garner, J. M. E. I. Du Pont de Nemours and
Company; U.S. Patent No. 5,710,344, January 20, 1998; Chem. Abstr.
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135
dx.doi.org/10.1021/cs500274n | ACS Catal. 2014, 4, 2130−2136

ACS Catalysis
Research Article
Boer, S.; Kuil, M.; Meeuwissen, J.; Breuil, P.-A. R.; Siegler, M. A.; Spek,
A. L.; Sandee, A. J.; De Bruin, B.; Reek, J. N. H. J. Am. Chem. Soc.
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35) Enhancing syngas pressure supports hydroformylation over
(
(
̈
ttger, D.; Kunze, C.;
̈
(
(
isomerization and hydrogenation as already found with nonfunction-
alized olefins: (a) Evans, D.; Osborn, J. A.; Wilkinson, G. J. Chem. Soc.
A 1968, 3133−3142. (b) Vilches-Herrera, M.; Domke, L.; Bo
ACS Catal. 2014, 4, 1707−1724.
36) When the reaction was carried out with an unmodified rhodium
̈
rner, A.
(
catalyst [1.0 mmol MO, 2.0 μmol Rh(acac)(CO) , 10 mL of toluene,
2
CO/H = 1:1, 20 bar, 80 °C, S:Rh = 500:1, 6 h], a conversion of 97%
2
of MO was noted. Besides 21.2% of ME, only 18.4% of the desired
product, MFS, yielded! The numerous other products could not be
clearly characterized up to now. This result gives clear proof for the
high chemoselectivity induced by the phosphoramidite ligands.
(
37) (a) Van Leeuwen, P. W. N. M.; Roobeek, C. F. J. Organomet.
Chem. 1983, 258, 343−350. (b) van Rooy, A.; Orij, E. N.; Kamer, P. C.
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Commun. 1991, 1096−1097. (c) Jongsma, T.; Challa, G.; van
Leeuwen, P. W. N. M. J. Organomet. Chem. 1991, 421, 121−128.
(
38) The reactions were started in a solvent without traces of acids.
However, it should be noted that in the result of the hydrolysis, a
heteroatom-substituted phosphine oxide (HASPO) is formed, which is
in equilibrium with its corresponding acid Christiansen, A.; Selent, D.;
Spannenberg, A.; Ko
̈
ckerling, M.; Reinke, H.; Baumann, W.; Jiao, H.;
Franke, R.; Borner, A. Chem.Eur. J. 2011, 17, 2120−2129 In this
̈
manner an autocatalytic reaction is initiated. However, because all
phosphoramidites tested give the same HASPO with water, this effect
is the same in all cases and can therefore neglected..
(
39) Remarkably, also the relevant precatalyst of 1a is stable at
elevated temperatures. Thus, treatment of [Rh(acac)(CO)(1a)] for 4
h at 80 or 100 °C in toluene, or at 140 °C in xylene did not change the
structure. Interestingly, by addition of 100 equivalents of water to a
0.0175 molar solution of the precatalyst in 1,4-dioxane, a new rhodium
complex of hitherto unknown structure was slowly formed in a yield of
31
3
2% [ P NMR (after addition of CD Cl ): δ 137.5 (d, J = 266 Hz]
2 2 PRh
within 27.5 h.
(
40) Thus, in the Rh-catalyzed hydroformylation of n-octenes
mixture of 3.3% 1-octene, 29.2% E/Z-2-octene, 29.2% E/Z-3-octene,
6.4% E/Z-4-octene, 2.1% structural isomers, 0.6% octane) with
ligands 1a−d the yields of aldehydes were in the following order: 1a
96%), 1b (98%), 1c (32%), 1d (20%).
(
1
(
2
136
dx.doi.org/10.1021/cs500274n | ACS Catal. 2014, 4, 2130−2136