Hydroformylation of 1-hexene catalyzed with rhodium fluorinated phosphine complexes in supercritical carbon dioxide and in conventional organic solvents: Effects of ligands and pressures

Article abstract of DOI:10.1039/b203657f

Rhodium-catalyzed hydroformylation of 1-hexene was investigated in compressed CO₂ and organic solvents using different fluorinated phosphine compounds as ligands at a temperature of 333 K. The reaction runs were conducted under conditions where the reaction mixtures were homogeneous in order to examine the activity of the rhodium complexes in different media. The effects of phosphine ligand, CO₂ pressure, syngas (H₂/CO) pressure and solvent on the hydroformylation activity were studied, along with FTIR examination of reaction mixtures. Such phosphine compounds as diphenyl(pentafluorophenyl)phosphine (II), bis(pentafluorophenyl)phenylphosphine (III), and tris(p-trifluoromethylphenyl)phosphine (VI) are effective ligands in scCO₂. Compound II is better since with it the undesirable isomerization side reaction is avoided. The n/iso ratio (heptanal/2-methylhexanal) does not change so much with the phosphine ligand used. It is interesting that the aldehyde yield goes through a minimum at about 9 MPa with increasing CO₂ pressure, and it tends to increase with an increase in the syngas pressure. The catalytic activities in scCO₂ are comparable with those in toluene and it is suggested that scCO₂ has some positive effects in promoting the hydroformylation.

Full text of DOI:10.1039/b203657f

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Hydroformylation of 1-hexene catalyzed with rhodium fluorinated
phosphine complexes in supercritical carbon dioxide and in
conventional organic solvents: effects of ligands and pressures
Shin-ichiro Fujita,a Shinya Fujisawa,a Bhalchandra M. Bhanage,ab Yutaka Ikushimabc and
Masahiko Arai*ab
a
Division of Materials Science and Engineering, Graduate School of Engineering,
Hokkaido University, Sapporo 060-8628, Japan. E-mail: marai@eng.hokudai.ac.jp
CREST, JST, Japan
Supercritical Fluid Research Center, Institute of Advanced Industrial Science and Technology,
Sendai 983-8551, Japan
b
c
Received (in Montpellier, France) 15th April 2002, Accepted 16th July 2002
First published as an Advance Article on the web 16th September 2002
Rhodium-catalyzed hydroformylation of 1-hexene was investigated in compressed CO2 and organic solvents
using different fluorinated phosphine compounds as ligands at a temperature of 333 K. The reaction runs were
conducted under conditions where the reaction mixtures were homogeneous in order to examine the activity of
the rhodium complexes in different media. The effects of phosphine ligand, CO2 pressure, syngas (H2/CO)
pressure and solvent on the hydroformylation activity were studied, along with FTIR examination of reaction
mixtures. Such phosphine compounds as diphenyl(pentafluorophenyl)phosphine (II),
bis(pentafluorophenyl)phenylphosphine (III), and tris(p-trifluoromethylphenyl)phosphine (VI) are effective
ligands in scCO2 . Compound II is better since with it the undesirable isomerization side reaction is avoided.
The n/iso ratio (heptanal/2-methylhexanal) does not change so much with the phosphine ligand used. It is
interesting that the aldehyde yield goes through a minimum at about 9 MPa with increasing CO2 pressure, and
it tends to increase with an increase in the syngas pressure. The catalytic activities in scCO2 are comparable with
those in toluene and it is suggested that scCO2 has some positive effects in promoting the hydroformylation.
Supercritical fluids have been attracting much attentions owing
to their unique physical and chemical properties.1 Supercritical
fluids may be used as reaction media, having such merits as
organic solvent replacement, better chemistry, and new chemi-
stry, and they will contribute environmentally benign methods
for chemical synthesis and processing. Highly pressurized car-
bon dioxide allows various chemical substances to dissolve in it
but it simply separates from them by depressurization. This
enables the easy separation of carbon dioxide used as a solvent
and/or a reactant from other reactants, products, and catalysts
that are liquid or solid. These features of carbon dioxide, in
addition to its harmless nature, are of industrial and academic
significance.
Organometallic complexes are effective catalysts for various
chemical transformations in conventional solvents.2 Several
research groups have studied the combination of these cata-
lysts and supercritical carbon dioxide (scCO2) with the inten-
tion of making better use of both their high activities and its
interesting properties.1 It is possible to conduct homogeneous
and heterogeneous catalytic reactions in scCO2 . For homo-
geneous reactions, organometallic complexes should show
the same catalytic performance as obtained in conventional
organic solvents but they should be soluble in scCO2 to a cer-
tain extent. Often used metal complexes include phosphine
compounds as ligands, which are less soluble in scCO2 . The
fluorination of phosphine ligands can, however, lead to an
increase in their solubility. According to Wagner et al.,3 for
example, the solubility of triphenylphosphine in scCO2 is
5.16 ꢀ 10ꢁ3 mol Lꢁ1 at 10.0 MPa and 310 K and, in contrast,
the solubility increases to 60 ꢀ 10ꢁ3 mol Lꢁ1 at 10.1 MPa and
310Kfortris(p-fluorophenyl)phosphineand228 ꢀ 10ꢁ3 molLꢁ1
at 9.5 MPa and 310 K for tris(pentafluorophenyl) phosphine.
The solubility of organometallic catalysts is a factor in deter-
mining the overall rate of homogeneous reactions but the rate
also depends on their specific activity. So, it is important to
examine such activity in the new reaction medium that is
scCO2 for various chemical transformations.
Recently, we have reported Heck reactions in scCO2 using
palladium complexes with several fluorinated phosphine com-
pounds, as shown later in Scheme 1, which showed significant
differences in their catalytic activity.4 In the present work, the
same phosphine compounds have been applied for another
type of chemical transformation, rhodium-catalyzed hydrofor-
mylation using 1-hexene as a substrate. Since CO and H2 gases
are present in addition to CO2 in hydroformylation reactions,
the environment around the organometallic catalysts is differ-
ent from that in Heck reactions and so the influence of the
phosphine ligands could be different. Several authors pre-
viously reported rhodium-catalyzed hydroformylation reac-
tions using fluorinated phosphine ligands in scCO2 .5–11 Palo
and Erkey studied the activities of rhodium complexes with
various fluorinated phosphine compounds for hydroformyla-
tion of 1-octene.5 They have reported that the activity depends
on the phosphine compound used and it increases with decreas-
ing basicity. Osuna et al.6 and Koch and Leitner7 investigated
hydroformylation of several olefins in scCO2 with rhodium cat-
alysts using variously modified phosphine ligands. Bach and
Cole-Hamilton studied hydroformylation of 1-hexene with
rhodium trialkylphosphine complexes in scCO2 and in toluene,
for which they reported similar TOF values.8 In the literature,
there are reported other works on hydroformylation reactions
12
in scCO2 and a few authors use heterogeneous catalysts.13
DOI: 10.1039/b203657f
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Scheme 2 Hydroformylation and isomerization of 1-hexene.
hydroformylation or isomerization, as shown in Scheme 2,
and the product distribution was observed to change depend-
ing on the catalysts and pressures of CO2 and syngas.
Reactions in scCO2
Figure 1 shows the results obtained at CO2 partial pressures of
8 MPa and 12 MPa and at a syngas partial pressure of 4 MPa.
The phosphine compounds used as ligands markedly change
the overall conversion of 1-hexene and the overall yield of
aldehydes, while they do not affect the 1 : 2 ratio so much.
The effectiveness of the ligands for the yield of aldehydes is
VI > II, III ꢂ V > no ligand ꢃ IV > I > VII at CO2 8 MPa
and VI > III > no ligand ꢃ IV ꢂ II > V > I > VII at CO2
12 MPa. The ligand VI is the most effective and the total alde-
hyde yield is about 65% with a 1 : 2 ratio of 2.3 but it also
causes the isomerization giving 3. Although the catalyst with
the ligand II is slightly less active than that with the ligand
VI, it gives little isomerization product 3. The other fluorinated
ligands, except for VII, are more effective compared with the
reference phosphine I. An increase in CO2 pressure has a sig-
nificant effect on the overall conversion only in two cases, with
Scheme 1 Phosphine compounds used as ligands in this work.
In the present work using such fluorinated phosphine com-
pounds as shown in Scheme 1, most of which are different from
those used in the above-mentioned previous works, the authors
have studied the effectiveness of these compounds in scCO2
and in organic solvents and the influence of CO2 and syngas
(CO/H2) pressures for the hydroformylation of 1-hexene. Pres-
sure effects have not been much studied so far in the literature.
Fig. 1 Influence of fluorinated phosphine ligands on hydroformyla-
tion and isomerization of 1-hexene in condensed carbon dioxide at
pressures of 8 MPa (a) and 12 MPa (b). Conditions: 1-hexene 0.318
mol Lꢁ1, Rh 2.47 ꢀ 10ꢁ2 mol Lꢁ1, ligand/Rh ¼ 4, syngas (CO/H2)
partial pressure 4 MPa, 333 K, 2 h. Products: 1: heptanal, 2:2-methyl-
hexanal, 3:2-hexene.
Results and discussion
Under the present conditions, the products heptanal (1),
2-methylhexanal (2), and 2-hexene (3) were formed from
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Fig. 2 Influence of CO2 pressure on hydroformylation and isomeri-
zation of 1-hexene catalyzed by Rh complexes with the ligands II (a)
and VI (b). Conditions: 1-hexene 0.318 mol Lꢁ1, Rh 2.47 ꢀ 10ꢁ2 mol
L
ꢁ1, ligand/Rh ¼ 4, syngas (CO/H2) partial pressure 4 MPa, 333 K,
2 h. Products: 1: heptanal, 2:2-methylhexanal, 3:2-hexene.
the ligand IV and without any ligand. For the other ligands,
the yields of aldehydes are similar at CO2 partial pressures
of 8 or 12 MPa. These effects of the phosphine compounds
and CO2 pressure observed are different from those previously
reported for Heck reactions.4
The influence of CO2 pressure has been examined with the
catalysts using the phosphine compounds II and VI at a syngas
partial pressure of 4 MPa. The results are given in Fig. 2, indi-
cating that the yield of aldehydes goes through a minimum at
about 9 MPa with CO2 pressure for the both catalysts although
the change is more significant for the phosphine II. For this
ligand, isomerization does not occur at CO2 pressures of
12 MPa or below while it proceeds at a higher CO2 pressure
of 20 MPa. For the phosphine VI, in contrast, the isomerization
can occur even at 8 MPa CO2 and the yield of the isomerization
product decreases slightly with CO2 pressure. Naked eye obser-
vations showed that the reaction mixtures were homogeneous at
pressures used in the experiments of Fig. 2. It was also observed
that solid rhodium complexes were seen to deposit after depres-
surization following the reactions only at a CO2 pressure of
9 MPa. It is speculated that at this pressure some fraction of
the catalysts precipitate from the CO2 solvent or metal com-
plexes such as dicabonyls are also formed. This causes a
decrease in the concentration of active species in the solvent,
giving drastic decreases in the yields of aldehydes; in the other
cases, the catalyst complexes were in the organic liquid phase
after the reaction experiments. Probably the solvent nature of
CO2 at 9 MPa is significantly different compared with that at
lower and higher pressures, resulting in the decrease in the yields
of aldehydes. With increasing CO2 pressure, the yields of alde-
hydes increase and show little change for the phosphines II and
VI, respectively. These types of pressure dependence are inter-
esting because the substrate and the catalyst are significantly
diluted with increasing CO2 pressure and thus the reaction
would be expected to slow down. This dilution effect is likely
to be cancelled or overcome by other effects; the details are
not known at present but highly dense CO2 should improve
the specific activity of the catalysts for hydroformylation.
Figure 3 shows the influence of the syngas partial pressure
for rhodium catalysts with the phosphines II and VI and
Fig. 3 Influence of syngas (CO/H2) pressure on hydroformylation
and isomerization of 1-hexene catalyzed by Rh precursor with no
phosphine ligands (a) and Rh complexes with the ligands II (b) and
VI (c). Conditions: 1-hexene 0.318 mol Lꢁ1, Rh 2.47 ꢀ 10ꢁ2 mol Lꢁ1
,
ligand/Rh ¼ 4, CO2 partial pressure 12 MPa, 333 K, 2 h. Products:
1: heptanal, 2: 2-methylhexanal, 3:2-hexene.
without any ligands at a CO2 partial pressure of 12 MPa.
For all the cases examined, the yield of aldehydes tends to
increase with the syngas pressure but the 1 : 2 ratio decreases.
This pressure dependence of the aldehyde yield is different
from that reported by Koch and Leitner,7 who indicate that
the yield decreases with the syngas pressure (3–6 MPa) for
hydroformylation of 1-octene in scCO2 . Compared with the
previous results with 1-octene and higher olefins,7,9 the extent
of isomerization is large in the present study with 1-hexene.
The pressure dependence of isomerization changes with the
phosphine used; the yield of 3 has a maximum at about
4 MPa in the absence of phosphines, slightly increases for
the phosphine II, but decreases for the phosphine VI. At a
higher syngas pressure of 8 MPa, a hydrogenated product of
hexane was observed to form in 10–15% yields, with a trace
amount of 3-methylhexanal, for all the ligands.
Concerning the influence of CO2 pressure, it should be noted
again that the yield of aldehydes, 1 + 2, is minimized near the
critical pressure of CO2 , as demonstrated in Fig. 2, in contrast
with previous observations reported in the literature. Several
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authors observed the occurrence of maximum reaction rates or
maximum conversions near the critical pressure for several
reactions.14 Although the present authors do not have a clear
explanation for the minimum observed, a possibility is given
hereafter, which invokes an inhibition effect of high CO con-
centration (pressure)10 and increased local concentration.15 It
is postulated that the local concentration of CO around the
rhodium complex catalyst is increased near the critical pressure
of CO2 and this decreases the rate of hydroformylation. In the
initial stage of reaction, the reaction mixture was seen to be
homogeneous in a single phase by naked eye observations,
even at CO2 pressures near the critical point. However, a frac-
tion of the rhodium complex catalysts could have changed dur-
ing the course of reaction due to the inhibition effect of CO and
they precipitated and separated as solids from the organic
liquid phase after reaction followed by depressurization, as
described above. The inhibition effect is typical of hydroformy-
lation kinetics in homogeneously catalyzed reactions with rho-
dium complex catalysts. Davis and Erkey reviewed the rate
expressions for hydroformylation of olefins in organic solvents
and scCO2 .10 There are large differences among the rate
expressions in the literature, indicating differences in the
mechanism and/or the rate-determining step, but these include
the inhibition effect at higher CO partial pressures. They dis-
cussed possible explanations for this CO inhibition effect on
the basis of a reaction mechanism. The local concentration
concept has been proposed to explain unexpected types of
behavior that are observed in supercritical fluids.15
above. With III (d), a shoulder is seen at 2009 cmꢁ1, in addi-
tion to the two large peaks at 2020 and 2089 cmꢁ1, and so
some metal precursors remained unchanged but the residual
ones complexed the phosphine III, producing more active spe-
cies. With II (c), V (f), and VI (g), in contrast, a single peak
exists at different positions of 1995, 1989 and 1996 cmꢁ1
,
respectively. So, active species were formed with the phos-
phines II, V, and VI, for which the rhodium complex with
the phosphine V is less active than those with the other two
phosphines. The spectrum (h) is very different from the other
spectra, having a peak at 1725 cmꢁ1 due to bridge-type carbo-
nyl. The phosphine VII may coordinate with the metal but the
complex formed is different from those with the phophines II,
III, V, and VI and it is much less active and its activity is com-
parable with that of the phosphine I.
According to Erkey and co-workers5,10 the basicity of the
ligand affects the electronic nature of the metal and the absorp-
tion of carbonyl would shift to higher frequency with a
decrease in the basicity. For the present cases in which
metal-phosphine complexes are formed, the basicity is
expected to be in the order of the phosphine VI, II > V, which
corresponds to the order of the hydroformylation activity at a
CO2 pressure of 12 MPa. So, when the basicity of the ligand is
weaker, the metal complex formed is more active in the present
cases as well. It is interesting that the metal complex with the
phosphine II is active for hydroformylation but it is much less
active for isomerization, in contrast to the complexes with the
phophines VI and V.
IR spectroscopy in scCO2
Reactions in organic solvents
Figure 4 shows FTIR spectra from 2200 to 1800 cmꢁ1 for the
catalytic species in scCO2 at CO2 and H2/CO partial pressures
of 12 MPa and 0.1 MPa, respectively. The absorbance with I
(b) is very weak and the spectra with no ligands (a) and IV
(e) have two peaks at 2020 and 2089 cmꢁ1 assigned to carbo-
nyl.5,16 The latter two spectra were found to be the same as
that of the rhodium precursor measured in air, indicating that
the phosphine IV did not complex the metal, in agreement with
the previous result of Palo and Erkey,5 and so the metal pre-
cursor remained unchanged. As a consequence, very similar
reaction results were obtained in the absence of any phos-
phines and in the presence of the phosphine IV, as described
The results in organic solvents and under solvent-less condi-
tions are shown in Fig. 5. The isomerization product was ana-
lyzed for the reactions in toluene and under solvent-less
conditions but not for the others due to limitation of the ana-
lysis. Relatively high yields of aldehydes were obtained for the
catalysts with the ligands II, V, and VI. The catalyst with the
ligand IV is also effective but only in toluene. In toluene,
hydroformylation took place but the isomerization did not
occur for the catalysts with the ligands IV and V, in contrast
to the results in scCO2 . The 1 : 2 ratio does not depend much
on the solvent used.
Fig. 4 FTIR spectra for Rh precursor with no phosphine ligands (a) and Rh complexes with the phosphines I (b), II (c), III (d), IV (e), V (f), VI
(g), and VII (h) in scCO2 at 333 K. Conditions: rhodium 2.59 ꢀ 10ꢁ3 ml Lꢁ1, phosphine/rhodium ¼ 4, CO2 12 MPa, syngas (CO/H2) 0.1 MPa.
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Fig. 5 Influence of fluorinated phosphine ligands on hydroformylation and isomerization of 1-hexene in different organic solvents: (a) toluene, (b)
ethyl acetate, (c) hexane, (d) without solvent. Conditions: 1-hexene 7.95 mol Lꢁ1, Rh 1.77 ꢀ 10ꢁ3 mol Lꢁ1 (a,b,c), 6.20 ꢀ 10ꢁ3 mol Lꢁ1 (d), ligand/
Rh ¼ 4, syngas (CO/H2) 4 MPa, 333 K, 2 h. Products: 1: heptanal, 2: 2-methylhexanal, 3: 2-hexene.
The influence of syngas pressure has been examined in
toluene in the presence of the phosphines II and VI and in
the absence of any phosphines (Table 1). The yield of alde-
hydes at 8 MPa is larger but the selectivity of 1 at 8 MPa is
smaller compared with those at a lower syngas pressure of
4 MPa. These trends are in agreement with those observed in
scCO2 .
hydroformylation of 1-hexene in scCO2 using Rh-P(C2H5)3
catalyst at a somewhat higher temperature of 363 K. Of
course, the TON and TOF values depend on reaction condi-
tions. The concentrations of the catalyst and the substrate in
scCO2 in mol Lꢁ1 are smaller by a factor of about 1/7 than
those in the organic solvents. This will decrease the total con-
version of the substrate in scCO2 ; however, the concentration
of the syngas is increased with disappearance of the gas–liquid
interface and complete dissolution of the syngas into the scCO2
solvent. This may partially explain that the total conversion
data in scCO2 and organic solvents are comparable. On the
basis of mole fraction, there are larger differences between
the organic solvents and scCO2 . Estimates of mole fractions
of reactants and catalyst are given in Table 2. It is again indi-
cated that scCO2 has a positive effect, enhancing the specific
activity of the catalysts, which exceeds the dilution effect with
increasing pressure.
Comparison between scCO2 and organic solvents
The results in scCO2 and organic solvents using the phosphine
compound VI are compared in Table 2. Under the conditions
used, the reaction was seen to occur in a single homogeneous
phase. The organic solvents except for NMP give only slightly
higher yields of aldehydes than scCO2 . Turnover numbers
(TON) for 2 h in scCO2 are 865 and 800 at CO2 partial pres-
sures of 8 and 12 MPa, respectively. In agreement with the pre-
vious report of Bach and Cole-Hamilton,8 these TON values
are comparable with those in organic solvents, for which
TON is 1031 in toluene, 918 in ethyl acetate and 990 in hexane.
Turnover frequency (TOF) in scCO2 is 433 hꢁ1 at 8 MPa and
400 hꢁ1 at 12 MPa. These TOF values are higher by about one
order of magnitude than those reported previously13 for
Conclusions
The present results demonstrate that the phosphine com-
pounds II, III, and VI are effective ligands for the rhodium
complexes that are active for the hydroformylation of 1-hex-
ene in scCO2 . Compound II is better in that the complex
formed catalyzes little isomerization. The 1:2 ratio does not
change much with the phosphine ligand used. The yield of
aldehydes (1 + 2) goes through a minimum at about 9 MPa
with increasing CO2 pressure. The yield of the isomerization
product 3 changes with CO2 pressure in different ways
depending on the phosphine ligand used. The yield of alde-
hydes tends to increase with an increase in the syngas (H2/
CO) pressure, while the yield of 3 changes differently with
the syngas pressure depending on the ligand used. The results
obtained in scCO2 are comparable with those in toluene and
it is suggested that scCO2 has some positive effects in pro-
moting the hydroformylation.
Table 1 Influence of syngas pressure on hydroformylation of 1-hex-
ene in toluenea
Yield of aldehydes (%)
Product ratio 1/2
Phosphine ligand 4 MPa
8 MPa
4 MPa
8 MPa
None
II
VI
25.7
69.3
80.4
57.4
79.7
85.1
2.13
1.94
2.65
1.42
1.65
1.70
a
Conditions: rhodium 1.77 ꢀ 10ꢁ3 mol Lꢁ1, 1-hexene 2.27 mol Lꢁ1
,
ligand/rhodium ¼ 4, temperature 333 K, time 2 h. Syngas: CO:H2
¼
1:1.
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Table 2 Comparison of yields of 1 + 2 and 3 in hydroformylation and isomerization of 1-hexene catalyzed with the Rh complex containing the
ligand VI, tris(p-trifluoromethyl phenyl) phosphine, in different solventsa
Concentration (mol Lꢁ1
)
Yield (%)
COb
1 + 2 (1/2)
3
b
Solvent
1-Hexene
Rh
H2
CO2 , 8 MPa
CO2 , 12 MPa
Toluene
0.318 (0.05)c
0.318 (0.03)c
2.27 (0.25)c
2.27
0.247 ꢀ 10ꢁ3 (4.0 ꢀ 10ꢁ5 c
)
0.761 (0.12)c
0.761 (0.12)c
67.2 (2.44)
62.2 (2.31)
80.4 (2.65)
71.6 (2.45)
77.2 (2.51)
0 (–)
20.1
16.5
14.5
–
0.247 ꢀ 10ꢁ3 (2.1 ꢀ 10ꢁ5 c
)
0.761 (0.06)c
0.761 (0.06)c
1.77 ꢀ 10ꢁ3 (1.9 ꢀ 10ꢁ4 c
)
0.032d (0.004)c
0.107d (0.012)c
Ethyl acetate
Hexane
NMP
1.77 ꢀ 10ꢁ3
1.77 ꢀ 10ꢁ3
1.77 ꢀ 10ꢁ3
–
–
–
–
–
–
2.27
2.27
–
–
a
b
Reaction conditions: 1-hexene/Rh ¼ 1280, syngas (H2/CO) 4 MPa, 333 K, time 2 h. Rough estimates based on van der Waals equations of
state for H2 and CO (ref. 17). c Mole fraction. The density of CO2 was obtained from ref. 18. d Estimates using Henry’s constants for H2 and CO
from ref. 19.
4
S. Fujita, K. Yuzawa, B. M. Bhanage, Y. Ikushima and M. Arai,
J. Mol. Catal. A: Chem., 2002, 180, 35.
Experimental
5
6
D. R. Palo and C. Erkey, Organometallics, 2000, 19, 81.
A. M. B. Osuna, W. Chen, E. G. Hope, R. D. W. Kemmitt, D. R.
Paige, A. M. Stuart, J. Xiao and L. Xu, J. Chem. Soc., Dalton
Trans., 2000, 4052.
D. Koch and W. Leitner, J. Am. Chem. Soc., 1998, 120, 13 398.
I. Bach and D. J. Cole-Hamilton, Chem. Commun., 1998, 1463.
D. R. Palo and C. Erkey, Ind. Eng. Chem. Res., 1998, 37, 4203.
Seven phosphine compounds, as shown in Scheme 1, were used
as ligands, of which the ligand VI was purchased from Strem
and the others from Aldrich. These were used without further
purification.
7
8
9
Hydroformylation experiments were conducted batchwise in
a 50 cm3 high-pressure stainless steel reactor with a magnetic
stirrer, a high-pressure liquid pump, and a back-pressure reg-
ulator.4,20 The reactor was charged with 1-hexene, Rh(acac)-
(CO)2 (both from Wako), and a phosphine ligand and heated
to a reaction temperature of 333 K using a water bath. Then
syngas (H2 : CO ¼ 1:1) was charged into the reactor to a cer-
tain pressure (4 MPa in many cases) followed by introduction
of liquid CO2 . The reaction was continued for 2 h. After the
reaction, the reactor was cooled by ice water to near room temp-
erature and depressurized with the back-pressure regulator.
The reaction mixture was analyzed by a gas chromatograph
packed with a capillary column using a flame ionization detec-
tor and a mass spectrometer.
10 T. Davis and C. Erkey, Ind. Eng. Chem. Res., 2000, 39, 3671.
11 G. Francio, K. Wittmann and W. Leitner, J. Organomet. Chem.,
2001, 621, 130; D. R. Palo and C. Erkey, Ind. Eng. Chem. Res.,
1999, 38, 3786; G. Francio and W. Leitner, Chem. Commun.,
1999, 1663; I. T. Horvath, G. Kiss, R. A. Cook, J. E. Bond,
P. A. Stevens, J. Rabai and E. J. Mozeleski, J. Am. Chem. Soc.,
1998, 120, 3133; S. Kainz, D. Koch, W. Baumann and W. Leitner,
Angew. Chem., Int. Ed. Engl., 1997, 36, 1628.
12 K. Wittmann, W. Wisniewski, R. Mynott, W. Leitner, C. L. Kra-
nemann, T. Rische, P. Eilbacht, S. Kluwer, J. M. Ernsting and
C. J. Elsevier, Chem.-Eur. J., 2001, 7, 4584; B. Guzel, M. A.
Omary, J. P. Fackler, Jr. and A. Akgerman, Inorg. Chim. Acta,
2001, 325, 45; Y. Guo and A. Akgerman, Ind. Eng. Chem. Res.,
1997, 36, 4581; J. W. Rathke, R. J. Klingler and T. R. Krause,
Organometallics, 1991, 10, 1350.
The phase behavior was examined with a 10 cm3 high-pres-
sure stainless steal reactor with sapphire windows and a mag-
netic stirrer. The reactor was charged with 1-hexene
(3.18 ꢀ 10ꢁ3 mol), Rh(acac)(CO)2 (2.48 ꢀ 10ꢁ6 mol), and a
phosphine ligand (9.92 ꢀ 10ꢁ6 mol) and heated to 333 K,
which was controlled with a heated oil circulating system.
Then the syngas was charged into the reactor and pressurized
by introducing liquid CO2 to a given pressure. The mixture in
the reactor was examined by the naked eye and also recorded
on a video recorder.
13 G. Snyder, A Tadd and M. A. Abraham, Ind. Eng. Chem. Res.,
2001, 40, 5317; S. Dharmidhikari and M. A. Abraham, J. Super-
crit. Fluids, 2000, 18, 1; M. S. Sellin and D. J. Cole-Hamilton,
J. Chem. Soc., Dalton Trans., 2000, 1681.
14 J. B. Ellington and J. F. Brennecke, J. Chem. Soc., Chem. Com-
mun., 1993, 1094; J. F. Brennecke, in Supercritical Engineering
Science. Fundamental Studies and Applications, eds. E. Kiran and
J. F. Brennecke, American Chemical Society, Washington, DC,
1993, p. 201; A. A. Clifford, in Supercritical Fluids: Fundamentals
for Applications, eds. E. Kiran and J. M. H. L. Sengers, NATO
ASI Series, Kluwer, Dordrecht, The Netherlands, 1994, p. 449;
P. E. Savage, S. Golapan, T. I. Mizan, C. J. Martino and E. E.
Brock, AIChE J., 1995, 41, 1723; Y. Ikushima, N. Saito, M. Arai
and H. W. Blanch, J. Phys. Chem., 1995, 99, 8941; Y. Ikushima,
N. Saito and M. Arai, J. Chem. Eng. Jpn., 1996, 29, 551; T. Sasa-
kura, Y. Saito, M. Okano, J. C. Choi and T. Sako, J. Org. Chem.,
2000, 63, 7095; H. Kawanami and Y. Ikushima, Chem. Commun.,
2000, 2089; S. Fujita, B. M. Bhanage, Y. Ikushima and M. Arai,
Green Chem., 2001, 3, 87.
The Rh complexes in scCO2 were examined with an in situ
FTIR using a 1.5 cm3 high-pressure cell with a path length
of
4 mm. The cell was charged with Rh(acac)(CO)2
(3.88 ꢀ 10ꢁ6 mol) and phosphine ligand (1.55 ꢀ 10ꢁ5 mol) fol-
lowed by introduction of the syngas (0.1 MPa) and liquid CO2
(14 MPa). The FTIR measurements were made at 333 K.
15 J. B. Ellington, K. M. Park and J. F. Brennecke, Ind. Eng. Chem.
Res., 1994, 33, 965; J. F. Brennecke, D. L. Tomasko, J. Peshkin
and C. A. Eckert, Ind. Eng. Chem. Res., 1990, 29, 1682; A. A.
Chialvo and P. G. Debenedetti, Ind. Eng. Chem. Res., 1992, 31,
1391; C. A. Eckert and B. L. Knutson, Fluid Phase Equilib.,
1993, 83, 93; T. W. Randolph, D. S. Clark, H. W. Blanch and
J. M. Prausnitz, Science, 1988, 239, 387; S. Kim and K. P. John-
ston, Ind. Eng. Chem. Res., 1987, 26, 1206.
16 K. Nakanishi, P. H. Solomon, Infrared Absorption Spectroscopy,
Holden-Day, San Francisco, CA, 2nd edn., 1977.
17 W. J. Moore, Physical Chemistry, Prentice-Hall, Englewood
Cliffs, NJ, 3rd edn., 1962.
18 T. Moriyoshi, T. Kita and Y. Uosaki, Ber. Bunsen-Ges. Phys.
Chem., 1993, 97, 589.
19 B. M. Bhanage, S. S. Divekar, R. M. Deshpande and R. V.
Chaudhari, J. Mol. Catal. A: Chem., 1997, 115, 247.
20 B. M. Bhanage, Y. Ikushima, M. Shirai and M. Arai, High Pres-
sure Res., 2001, 20, 131.
References
1
Chemical Synthesis Using Supercritical Fluids, eds. P. G. Jessop
and W. Leitner, Wiley-VCH, Weinheim, 1999; P. G. Jessop,
T. Ikariya and R. Noyori, Chem. Rev., 1999, 99, 475; W. Tumas,
in Proceedings of the 5th International Symposium on Supercritical
Fluids, Atlanta, USA, 2000; R. S. Oakes, A. A. Clifford and C. M.
Rayner, J. Chem. Soc., Perkin Trans. 1, 2001, 917; B. M. Bhanage
and M. Arai, Catal. Rev. Sci. Eng., 2001, 43, 315.
2
3
Applied Homogeneous Catalysis with Organometallic Compounds,
eds. B. Cornils and W. A. Herrmann, Wiley-VCH, Weinheim,
2000; Metal-catalyzed Cross-coupling Reactions, eds. F. Dietrich
and P. J. Stang, Wiley-VCH, Weinheim, 1998; W. A. Herrmann
and B. Cornils, Angew. Chem., Int. Ed. Engl., 1997, 36, 1048.
K.-D. Wagner, N. Dahmen and E. Dinjus, J. Chem. Eng. Data,
2000, 45, 672.
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New J. Chem., 2002, 26, 1479–1484