Hydroformylation of 1-octene in supercritical carbon dioxide with alkyl P-donor ligands on rhodium using a peracetylated β-cyclodextrin as a solubiliser

Article abstract of DOI:10.1002/ejic.200800153

The presence of peracetylated β-cyclodextrin in the reaction medium allowed for an increase in the solubility of rhodium species modified by alkyl P-donor ligands in the catalytic hydroformylation of 1-octene in supercritical carbon dioxide. These results were explained by considering an interaction between the peracetylated β-cyclodextrin and the P-donor ligands. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200800153

FULL PAPER
DOI: 10.1002/ejic.200800153
Hydroformylation of 1-Octene in Supercritical Carbon Dioxide with Alkyl
P-Donor Ligands on Rhodium Using a Peracetylated β-Cyclodextrin as a
Solubiliser
Clara Tortosa Estorach,[a] Marta Giménez-Pedrós,[a] Anna Maria Masdeu-Bultó,*[a]
Adlane D. Sayede,[b] and Eric Monflier*[b]
Keywords: Hydroformylation / Supercritical carbon dioxide / Rhodium / Cyclodextrins / P ligands
The presence of peracetylated β-cyclodextrin in the reaction
medium allowed for an increase in the solubility of rhodium
species modified by alkyl P-donor ligands in the catalytic hy-
droformylation of 1-octene in supercritical carbon dioxide.
These results were explained by considering an interaction
between the peracetylated β-cyclodextrin and the P-donor
ligands.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
phase reactant concentrations would be higher in it than in
organic solvents.[4]
Introduction
Hydroformylation involves the addition of carbon
monoxide and hydrogen to a carbon–carbon double bond
to form the corresponding linear and branched aldehydes.
The reaction (Scheme 1) is mostly accomplished with a rho-
dium- or cobalt-based catalyst.[1] The main products are
used for the production of alcohols, carboxylic acids, aldol
products, diols, acetals, ethers, acroleins and esters.[2] Speci-
fically, the hydroformylation of 1-octene is performed in the
production of plasticizer alcohols and biodegradable deter-
gents.[1]
Unfortunately, ionic and polar reagents are generally not
very soluble in scCO2, which restricts its application in cata-
lytic processes.[4] To overcome this limitation, ligands modi-
fied by the incorporation of perfluorinated chains,[5] polysil-
anes[6] and carbonyl groups[7] have been employed. Other
possibilities include the use of soluble surfactants or mass
transfer agents, which induce the formation of micelles with
a high-density fluid phase[8,9] and thus increase the solubil-
ity of the catalyst in the scCO2.
It has recently been reported that peracetylated cyclodex-
trin exhibits a high degree of miscibility with dense CO2
over a broad range of concentrations.[10] Interestingly,
Monflier et al. have recently demonstrated that peracety-
lated β-cyclodextrin has a great ability to form inclusion
complexes with various arylphosphanes in a scCO2 me-
dium.[11] A similar phenomenon had also been observed
with sulfonated arylphosphanes in water by using hydro-
soluble cyclodextrins.[12]
Scheme 1. Hydroformylation of 1-octene.
In a previous work we reported the use of P-donor li-
gands (1–3, Figure 1) containing a branched alkylic chain
in the hydroformylation of 1-octene in supercritical carbon
The application of supercritical carbon dioxide (scCO2)
as a reaction medium in homogeneous catalysis has been
investigated by a number of research groups in recent years
since it is inert, nontoxic, nonflammable, cheap, readily
available and environmentally acceptable.[3] In addition,
gases are completely miscible with scCO2; therefore, gas-
[a] Departament de Química Física i Inorgànica, Universitat Ro-
vira i Virgili,
Marcel.li Domingo s/n, 43007 Tarragona, Spain
Fax: +34-977-559563
E-mail: annamaria.masdeu@urv.net
Figure 1. P-donor ligands containing a branched alkylic chain used
in the hydroformylation of 1-octene in scCO2: phosphite ligand (1),
phosphonite ligand (2) and phosphinite ligand (3).
[b] Université d’Artois, Unité de Catalyse et de Chimie du Solide,
UMR CNRS 8181, Faculté des Sciences Jean Perrin,
Rue Jean Souvraz SP 18, 62307 Lens Cédex, France
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A. M. Masdeu-Bultó, E. Monflier et al.
FULL PAPER
dioxide. These ligands formed rhodium catalytic systems
In this context, the ability of Per-Ac-β-CD to form in-
that were not soluble in scCO2. Despite this fact, conver- clusion complexes with ligands 1–3 was investigated by per-
sions up to 82% and selectivities up to 94% were achieved forming quantum chemical calculations on the Per-Ac-β-
using these systems.[13] Therefore, we considered the pos- CD/ligand systems.
sibility of increasing the solubility of these catalytic systems
in scCO2 by forming inclusion complexes between the per- was constructed using geometries separately optimised for
acetylated cyclodextrin and the ligands. Per-Ac-β-CD and for 1. The glycosidic oxygen atoms of
For the Per-Ac-β-CD/1 system, the inclusion complex
Here we present the hydroformylation of 1-octene with Per-Ac-β-CD were placed onto the XY plane and their cen-
the [Rh(acac)(CO)2] catalytic system associated with tre was defined as the centre of the coordination system.
branched alkyl phosphite, phosphonite and phosphinite li- The complexation of 1 was then investigated by moving one
gands (1–3, Figure 1) in supercritical carbon dioxide with of its alkylic chains along the Z axis at fixed increments of
a peracetylated cyclodextrin as a mass transfer promoter 0.2 Å. All energy minimizations were performed without
(Figure 2).
any geometry constraints. Two different inclusion orienta-
tions were considered: the orientation in which 1 points to-
ward the narrower native β-CD ring (containing 7 acetyl
groups), indicated here as the primary rim, and the other
in which 1 points toward the wider native β-CD rim (con-
taining 14 acetyl groups), indicated here as the secondary
rim. Figure 3 depicts the stabilisation energy variation of
the inclusion processes of 1 with Per-Ac-β-CD at different
distances and orientations.
Figure 2. Peracetylated cyclodextrin (Per-Ac-β-CD).
Results and Discussion
Ligands 1–3 were synthesised as reported by Giménez
et al. by the reaction of the commercially available 3,5,5-
trimethylhexanol with phosphorus trichloride or the corre-
sponding chlorophenylphosphane in diethyl ether in the
presence of pyridine.[13] Peracetylated β-cyclodextrin was
purchased from Aldrich Chemicals and used without fur-
ther purification. This CD is a cyclic oligosaccharide com-
posed of seven -glucopyranose residues linked by α-(1,4)
bonds. Each glucopyranose unit was fully acetylated.
Figure 3. Graphic diagram for the inclusion process of the phos-
phite 1 with Per-Ac-β-CD through the primary (᭡) and secondary
(᭿) faces.
Inclusion Studies
As the formation of inclusion complexes is difficult to
In both cases, favourable interactions take place between
prove experimentally in supercritical conditions, some the two species. The energy of the complex decreases as the
attempts to observe the interaction between ligand 1 and alkylic chain enters into the Per-Ac-β-CD cavity, and again
Per-Ac-β-CD were performed by using toluene as a solvent increases because of crowding (i.e. steric hindrance) be-
instead of supercritical CO2. Unfortunately, the formation tween the alkylic chains remaining outside the cavity and
of inclusion species in toluene was rejected by analysing the the acetyl groups of the Per-Ac-β-CD rims. However, we
reactivity of the [Rh(acac)(CO)2]/1 system in the presence notice that the more favourable minimum energy structure
of Per-Ac-β-CD with CO and H2 with high-pressure NMR of the Per-Ac-β-CD/1 complex occurs through the second-
spectroscopy. Indeed, the species detected in these condi- ary rim. Figure 4 (a) displays the computer-generated struc-
tions were comparable to the ones reported by us without ture of this complex.
the cyclodextrin:[13] the major species observed in the
The energy variation involved in the inclusion emulsion
31P{1H} and 1H NMR spectra were [RhH(CO)(1)3] and indicates that the complexes prefer to adopt an inclusion
[RhH(CO)2(1)2]. It must be noted that this result is not sur- geometry with the alkyl chain inside the host cavity in order
prising as the formation of inclusion complexes in organic to increase the van der Waals attraction between the host
media is seldom observed with cyclodextrin derivatives be- and guest. This is supported by the van der Waals surfaces
cause of the lack of hydrophobic forces. Nevertheless, in- of the Per-Ac-β-CD/1 complex [see Figure 4 (b and c)],
clusion complexes may be formed in scCO2.
where one can clearly see that the alkylic chain of the phos-
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Hydroformylation of 1-Octene in scCO2
Solubility Studies
As ligand 1 has the greater ability of interaction with the
Per-Ac-β-CD, solubility studies were performed with it. The
solubility of the new [Rh(acac)(CO)2]/1/Per-Ac-β-CD cata-
lytic system was studied in an autoclave equipped with view
windows. In a previous work, we observed by visual inspec-
tion through the windows of the autoclave that the
[Rh(acac)(CO)2]/1–3 catalytic systems had no apparent sol-
ubility in scCO2 up to 240 atm and 80 °C.[13] When similar
solubility studies were performed with [Rh(acac)(CO)2]
(6ϫ10–3 ), ligand 1 (P/Rh = 6) and Per-Ac-β-CD (Per-
Ac-β-CD/Rh = 6) in the autoclave with CO/H2 at 20 atm
and 80 °C, we observed at 140 atm the formation of an ini-
tial suspension, which at 250 atm turned into an orange-
coloured solution (Figure 6) (solubility of at least
6ϫ10–3 ). The presence of the Per-Ac-β-CD favoured the
solubility of the species formed under hydroformylation
conditions in scCO2.
Figure 4. (a) Side view of the computer-generated structure of the
Per-Ac-β-CD/1 inclusion complex. (b) Side view and (c) bottom
view of the van der Waals surfaces of the Per-Ac-β-CD/1 inclusion
complex.
phite 1 fits tightly in the Per-Ac-β-CD cavity, which leads
to the formation of stable inclusion complexes.
For ligands 2 and 3, calculations also confirm that Per-
Ac-β-CD can host an alkylic chain of the ligand in its cav-
ity. Figure 5 shows the most stable computer-generated
structure of the Per-Ac-β-CD/2 and Per-Ac-β-CD/3 in-
clusion complexes.
Figure 6. View of the autoclave window for the [Rh(acac)(CO)2]/1/
Per-Ac-β-CD system at 80 °C and at (a) 200 atm and (b) 250 atm
(solubilised).
Hydroformylation of 1-Octene
We performed the catalytic hydroformylation of 1-octene
using the in situ formed catalyst precursor [Rh(acac)(CO)2]/
1–3 with the addition of peracetylated β-cyclodextrin. The
results are summarised in Table 1.
The addition of Per-Ac-β-CD has a positive effect on the
total conversion when the reaction is performed at condi-
tions of partial solubility (167 atm) (from 49% in entry 1
to 96% in entry 2, Table 1), although the chemoselectivity
in aldehydes decreases to 77%. An increase in the amount
of internal aldehydes associated with olefin isomerisation
was also observed (entry 2, Table 1). The reaction rate in-
crease was attributed to a higher solubility of rhodium spe-
Figure 5. Side view of the computer-generated structure of the (a)
Per-Ac-β-CD/2 and (b) Per-Ac-β-CD/3 inclusion complexes.
The possibility of including one of the ligand’s aromatic cies in the reaction medium because of the formation of
rings into the Per-Ac-β-CD cavity was also investigated and inclusion complexes between ligand 1 and Per-Ac-β-CD.
calculations indicated that this could hardly occur.
However, the selectivity decrease suggests strongly that the
By comparing Figures 4 and 5, it is clear that ligand 1 is catalytically active species in the presence of Per-Ac-β-CD
positioned more deeply in the Per-Ac-β-CD cavity than li- are different from those observed without cyclodextrin.
gands 2 and 3, which strongly suggests that the Per-Ac-β-
When the reaction is performed under homogeneous
CD/1 inclusion complex is more stable than the two others. conditions (250 atm), the effect of the addition of Per-Ac-
The shallower penetration of ligands 2 and 3 into the CD β-CD depends on the temperature and CD/Rh ratio. At
cavity is likely a consequence of the steric hindrance be- 100 °C the conversion and the selectivity decrease (entries
tween the external aromatic ring and the β-CD border.
3 and 4, Table 1). The decrease in conversion could be due
Eur. J. Inorg. Chem. 2008, 2659–2663
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A. M. Masdeu-Bultó, E. Monflier et al.
FULL PAPER
Table 1. Hydroformylation of 1-octene using [Rh(acac)(CO)2]/L(1–3)/Per-Ac-β-CD in scCO2.[a]
[b]
[d]
Entry
L
CD/Rh T [°C]
PCO [atm] PH2 [atm]
PTOT [atm] % Conv.[c] % Sa
n/iso/int[e]
% Si[f]
1[g]
2
1
1
1
1
–
1
1
1
1
1
2
3
0
6
0
6
–
0
6
12
6
6
6
6
100
100
100
100
80
80
80
80
80
80
80
10
10
10
10
10
10
10
10
2.5
10
10
10
10
10
10
10
10
10
10
10
2.5
10
10
10
167
167
250
250
250
250
250
250
250
250
250
250
49
96
82
71
99
98
87
39
25
23
65
98
90
77
89
71
20
76
84
20
64
80
75
54
80:20:–
45:33:22
78:22:–
80:17:3
28:42:30
77:22:1
75:24:1
67:33/–
70:12:18
26:48:26
44:40:16
48:37:15
10
22
11
29
80
24
16
80
36
20
25
46
3[g]
4
5
6
7
8
9
10[h]
11
12
80
[a] Reaction conditions: scCO2: [Rh(acac)(CO)2] = 0.06 mmol; Rh/L = 6, L = 0.36 mmol; 1-octene = 12 mmol; 1-octene/Rh = 200; V =
25 mL; t = 3 h. [b] Total pressure. [c] Total conversion by GC. [d] Selectivity for aldehydes. [e] int = 3-ethylheptanal and 4-propylhexanal.
[f] Selectivity for internal octenes. [g] Ref.[13] [h] substrate = trans-2-octene.
to a dilution effect. Upon decreasing the temperature to
Conclusions
80 °C, the addition of Per-Ac-β-CD has an opposite effect:
Peracetylated β-cyclodextrin greatly affects the catalytic
the selectivity improves but the total conversion is ca. 10%
behaviour of rhodium complexes modified by branched alk-
lower than without the cyclodextrin (entries 6 and 7,
ylic phosphite ligands in scCO2. The addition of peracety-
Table 1). It should be noticed that the regioselectivity (n/iso
lated β-cyclodextrin has a positive effect on the solubility of
= 3.5) was of the order expected for this kind of P-donor
the catalytic systems through an interaction with the ligand.
ligand,[1b] which suggests that Per-Ac-β-CD did not greatly
Nevertheless, this interaction could lead to the formation
modify the nature of the catalytically active species under
of low coordination phosphane rhodium species. This phe-
these conditions. However, when the reaction was per-
nomenon was explained by a displacement of the equilibria
formed at a higher CD/Rh ratio, the conversion and selec-
between the various rhodium species.
tivity decreased to 39 and 20% respectively (entry 8,
Table 1), which suggests that species without coordinated
ligands could be formed at high CD/Rh ratios. This hypoth-
esis was supported by an experiment performed without
any ligand. Indeed, the aldehyde selectivity was close to
Experimental Section
General: Reagents were purchased from Aldrich and Fluorochem
and used without further purification. 1-octene was filtered
those obtained with CD/Rh = 12 (entry 8 vs. 5, Table 1).
through alumina before use. Carbon dioxide (SCF Grade,
As observed in conditions of partial solubility, the ex-
99.999%) was supplied by Air Products, carbon monoxide
periments conducted in homogeneous conditions indicate
that the addition of Per-Ac-β-CD modifies the nature of
the catalytically active species. In fact, the interaction of the
Per-Ac-β-CD with 1 likely induced a shift of the equilib-
rium between the various rhodium species towards the for-
mation of low coordination phosphane rhodium species
which are responsible for the formation of the isomerised
olefins. It should be noticed that a similar but less marked
phenomenon was also observed in the aqueous/organic bi-
phasic hydroformylation reaction promoted by methylated
β-cyclodextrins.[14]
Since we observed a significant amount of isomerisation,
we used the [Rh(acac)(CO)2]/1/Per-Ac-β-CD system under
the same conditions in the hydroformylation of trans-2-oc-
tene. In this experiment the distribution of aldehydes (entry
10, Table 1) indicates that the isomerisation rate is slower
than the hydroformylation rate for this system.
(99.99%) was supplied by Air Liquid and hydrogen C-50 was sup-
plied by Carburos Metalicos.
Safety Warning: Experiments involving pressurised gases can be
hazardous and must be conducted with suitable equipment and
under the appropriate safety conditions only.
High-pressure NMR experiments (HPNMR) were carried out in a
10-mm-diameter sapphire tube with a titanium cap equipped with
Teflon/polycarbonate protection.[15]
Gas chromatography analyses were performed with a Hewlett–
Packard 5890A apparatus in an HP-5 (5% diphenylsilicone/95%
dimethylsilicone) column (25 mϫ0.2 mm) for the separation of the
products and undecane was added as an internal standard after the
reaction.
Calculations: Calculations were performed at the PM3 level of
theory using the GAUSSIAN 03 program.[16] The initial geometries
were constructed with the help of the Molden program,[17] as pre-
viously reported.[18]
When the [Rh(acac)(CO)2]/2 or 3/Per-Ac-β-CD systems
were used, the conversion obtained was better in the case
of 2 and was of the same order for the catalytic system with
ligand 3 compared with the analogous systems without the
cyclodextrin. Unfortunately, the selectivity in aldehydes was
not improved (entries 11 and 12, Table 1).[13]
Catalysis: Hydroformylation experiments were carried out in a Parr
autoclave (25 mL) with magnetic stirring. The autoclave was
equipped with a liquid inlet, a gas inlet, a CO2 inlet and a thermo-
couple. An electric heating mantle kept the temperature constant.
Standard Hydroformylation Experiment in scCO2: The [Rh(acac)-
(CO)2] complex (0.06 mmol) and the peracetylated cyclodextrin
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Hydroformylation of 1-Octene in scCO2
[6] a) M. F. Sellin, I. Bach, J. M. Webster, F. Montilla, V. Rosa, T.
Avilés, M. Poliakoff, D. J. Cole-Hamilton, J. Chem. Soc., Dal-
ton Trans. 2002, 4569–4576; b) F. Montilla, V. Rosa, C. Prevete,
T. Avilés, M. Nunes da Ponte, D. Masi, C. Mealli, Dalton
Trans. 2003, 2170–2176; c) F. Montilla, A. Galindo, R. Andrés,
M. Córdoba, E. de Jesús, C. Bo, Organometallics 2006, 25,
4138–4143.
[7] a) Y. Hu, W. Chen, L. Xu, J. Xiao, Organometallics 2001, 20,
3206–3208; b) C. D. Ablan, D. Sheppard, E. J. Beckman,
M. M. Olmstead, P. G. Jessop, Green Chem. 2005, 7, 590–594.
[8] J. Eastoe, A. Dupont, D. C. Steytler, Curr. Opin. Colloid Inter-
face Sci. 2003, 8, 267–273.
[9] G. B. Jacobson, C. T. Lee, K. P. Johnston, J. Org. Chem. 1999,
64, 1201–1206.
[10] a) V. K. Potluri, J. Xu, R. Enick, E. Beckman, A. D. Hamilton,
Org. Lett. 2002, 4, 2333–2335; b) V. K. Potluri, A. D. Hamil-
ton, C. F. Karanikas, S. E. Bane, J. Xu, E. J. Beckman, R. M.
Enick, Fluid Phase Equilib. 2003, 211, 211–217.
[11] a) G. Filardo, M. Di Blasi, A. Galia, A. Ponchel, H. Bricout,
A. D. Sayede, E. Monflier, J. Supercrit. Fluids 2006, 36, 173; b)
A. Galia, E. C. Navarre, O. Scialdone, M. Ferreira, G. Filardo,
S. Tilloy, E. Monflier, J. Phys. Chem. B 2007, 111, 2573.
[12] a) M. Canipelle, L. Caron, C. Christine, S. Tilloy, E. Monflier,
Carbohydr. Res. 2002, 337, 281–286; b) L. Caron, C. Christine,
S. Tilloy, E. Monflier, D. Landy, S. Fourmentin, G. Surpate-
anou, Supramol. Chem. 2002, 14, 11–20; c) E. Monflier, S. Til-
loy, C. Méliet, A. Mortreux, D. Landy, S. Fourmentin, G. Sur-
pateanou, New J. Chem. 1999, 23, 469–472.
(Per-Ac-β-CD) (0.36 mmol) were introduced into the evacuated au-
toclave. Then the autoclave was purged with nitrogen/vacuum cy-
cles. After that, 1-octene (12 mmol) and the ligand (0.36 mmol)
were added. The system was pressurised with 20 atm of CO/H2
(1:1), and liquid CO2 was introduced until a total pressure of 60 bar
was reached. The autoclave was heated to the desired temperature.
When thermal equilibrium was reached, the total pressure was ad-
justed with a Thar syringe pump. After the reaction time, the auto-
clave was cooled down to 0 °C and depressurised. Undecane was
added to the final mixture and this was analysed by GC. The prod-
ucts were identified by GC/MS.
Solubility Studies: The solubility studies were carried out in a Thar
reactor (100 mL) equipped with sapphire windows and magnetic
stirring. The autoclave was charged with the ligand (0.33 mmol),
the [Rh(acac)(CO)2] (0.055 mmol) and the Per-Ac-β-CD. The auto-
clave was purged with nitrogen/vacuum cycles. Then, the reactor
was pressurised with CO, H2 and CO2. The system was heated to
80 °C, and the total pressure was increased gradually up to
250 atm. The solubility was monitored by visual inspection through
the sapphire windows with a mirror due to safety requirements.
HPNMR: In a typical experiment, the NMR tube was filled under
N2 with a solution of [Rh(acac)(CO)2] (0.04 mmol), the ligand 1
(0.24 mmol), the Per-Ac-β-CD (0.24 mmol) and [D8]toluene
(2 mL). The tube was pressurised to 20 atm of CO/H2 (1:1) and left
at 70 °C for 1 h. The NMR spectra were then recorded.
[13] M. Gimenez-Pedrós, A. Aghmiz, N. Ruiz, A. M. Masdeu-
Bultó, Eur. J. Inorg. Chem. 2006, 1067–1075.
[14] E. Monflier, H. Bricout, F. Hapiot, S. Tilloy, A. Aghmiz, A. M.
Masdeu-Bultó, Adv. Synth. Catal. 2004, 346, 425–431.
[15] A. Cusanelli, U. Frey, D. T. Richens, A. Merbach, J. Am.
Chem. Soc. 1996, 118, 5265–5271.
Acknowledgments
We gratefully acknowledge the Generalitat de Catalunya (DURSI
and Fons Social Europeu) for a Fellowship (FI) to C. T. and
2005SGR00777, the Ministerio de Educacion y Ciencia (MEC)
(CTQ2004-03831/PPQ, CSD2006-0003) for financial support.
[16] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, J. A. M. Junior, T. Vreven, K. N.
Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tomasi, V.
Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A.
Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R.
Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O.
Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian,
J. B. Cross, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Strat-
mann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador,
J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Dan-
iels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K.
Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Ba-
boul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Lia-
shenko, P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T.
Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, M.
Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W.
Wong, C. Gonzalez, J. A. Pople, GAUSSIAN 03 program,
Gaussian, Inc., Pittsburgh PA, 2003.
[1] a) C. D. Frohning, C. W. Kohlpaintner, in Applied Homogen-
eous Catalysis with Organometallic Compounds (Eds.: B.
Cornils, W. A. Herrmann), VCH, Weinheim, 1996, ch. 2.1, pp.
29; b) P. W. N. M. van Leeuwen, C. Claver (Eds.), Rhodium
Catalyzed Hydroformylation, Kluwer Academia Publishers,
Dordreht, 2000.
[2] A. M. Trzeciak, J. J. Ziółkowski, Coord. Chem. Rev. 1999, 190–
192, 883–900.
[3] P. G. Jessop, W. Leitner (Eds.), Chemical Synthesis Using Su-
percritical Fluids, Wiley-VCH, Weinheim, New York, 1999.
[4] a) P. G. Jessop, T. Ikariya, R. Noyori, Chem. Rev. 1999, 99,
475–493; b) W. Leitner, Acc. Chem. Res. 2002, 35, 746–756; c)
D. J. Cole-Hamilton, Science 2003, 299, 1702–1706; d) P. G.
Jessop, J. Supercrit. Fluids 2006, 38, 211–231.
[5] Some examples are found in: a) S. Kainz, D. Koch, W. Baum-
ann, W. Leitner, Angew. Chem. Int. Ed. Engl. 1997, 36, 1628–
1630; b) A. M. Banet Osuna, W. Chen, E. G. Hope, R. D. W.
Kemmitt, D. R. Paige, A. M. Stuart, J. Xiao, L. Xu, J. Chem.
Soc., Dalton Trans. 2000, 4052–4055; c) D. R. Palo, C. Erkey,
Organometallics 2000, 19, 81–86.
[17] G. Schaftenaar, J. H. Noordik, J. Comput. Aid. Mol. Des. 2000,
14, 123–134.
[18] A. D. Sayede, A. Ponchel, G. Filardo, A. Galia, E. Monflier, J.
Mol. Struct. 2006, 777, 99–106.
Received: February 11, 2008
Published Online: April 29, 2008
Eur. J. Inorg. Chem. 2008, 2659–2663
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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